The Scientific Panel on Food Additives, Flavourings, Processing Aids and Materials in

Contact with Food (AFC) has been asked to evaluate the food safety aspects related to the removal of fluoride from natural mineral waters (NMWs) by filtration through a bed of activated alumina.

NMWs at source may contain levels of fluoride higher than the maximum concentration limits established for the constituents of natural mineral waters by the Commission Directive 2003/40/EEC. Removal of the fluoride is only allowed by an authorised process.

Information concerning the source and treatment of activated alumina and the filtration process conditions was provided and showed that critical steps of the proposed process are the following:

•  Testing of activated alumina filter according to the European standard applicable for leaching tests (EN 12902) [6] to ensure that no impurities are leached to the water in quantities that result in concentrations exceeding the limits set in Commission Directive 2003/40/EC on the constituents of natural mineral waters, or in the absence of relevant limits in that Directive, the restrictions set in Council Directive 98/83/EC on the quality of water intended for human consumption or in national applicable legislation.
•  Initialisation procedure with alkaline or acidic chemicals to remove any impurities and fine particles before the use of the filter.
•  Regeneration procedure with appropriate chemicals to renew the capacity of the filter resulting at the same time in the removal of any possibly formed biofilm.

From the information provided it was shown that under optimised process conditions the release of impurities due to the use of the activated alumina, if it occurs at all, is always lower than the relevant limits set in the Directives mentioned above. In addition, due to the regular regeneration process of the activated alumina according to Good Manufacturing Practice (GMP) and the principles of Hazard Analysis and Critical Control Points (HACCP), there is no additional risk of microbial contamination.

http://www.efsa.eu.int/science/afc/catindex_en.html

It was also demonstrated that fluoride can be removed effectively from NMWs by filtration through a bed of activated alumina. To maintain compliance with the limits set in Directive 2003/40/EC the fluoride content of the treated water needs to be monitored due to the reducing absorption capacity of the activated alumina during the cycle of use and regeneration.

The Panel concluded that the removal of fluoride from NMWs by filtration through activated alumina can be safely applied provided the critical steps as described above are implemented and monitored appropriately.

KEY WORDS

Fluoride removal, activated alumina, natural mineral waters.

BACKGROUND

Council Directive 80/777/EEC  lays down the provisions applicable to the exploitation and marketing of natural mineral waters (NMWs). NMWs are characterised by their constant chemical composition, of so-called “essential  constituents”  which  are supposed to have a beneficial effect on the human organism. NMWs sources have to be continuously kept free from any environmental contamination (microbiological and chemical contaminants) because of their underground origin and the required measures of protection of the sources. Therefore, treatments for the removal of a microbiological or chemical contamination are not allowed by the E.U. NMW legislation. However, for technological and food safety purposes a limited number of treatments may be used,e.g. removal of unstable elements (iron, sulphur and manganese compounds) by precipitation, filtration or treatment with ozone-enriched air without changing the composition of the NMWs as regards the essential constituents. Such  treatments should be notified to and controlled by competent authorities.

NMWs may also contain so-called “undesirable constituents” which, though naturally present may have undesirable effects on public health. NMWs shall  be  “suitable’  for human consumption at source, but do not have to comply with the maximum limits for constituents and residues applicable to drinking waters.

In 2003, the Commission adopted Commission Directive 2003/40/EC2 which established an exhaustive list of undesirable constituents and related maximum limits. In the case of fluoride, Directive 2003/40/EC states both a maximum limit of 5 mg/l (applicable from 1st January 2008) and a labelling requirement (applicable from 1st July 2004): “contains more than 1.5 mg/l of fluoride: not suitable for regular consumption by infants and children under 7 years of age” The maximum limit will be re-examined on the basis of the EFSA opinion.

Where maximum limits for undesirable constituents in NMWs are exceeded, operators shall put in place a treatment approved by the Commission to remove them totally or partially. Article 4 of Directive 80/777/EEC lays down the mandatory requirements applicable to each removal treatment that operators can put in place:

• It complies with the conditions of use which have been adopted by the Commission (so-called “EU approval”), following EFSA consultation (Article 4.1b and 4.1c);
•  It does not alter the composition of the water as regards the “essential constituents” (Article 4.1);
•  It may not be subject of any addition other than the introduction  or  re- introduction of carbon dioxide (Article 4.2)
•   It does not lead to any disinfection action (Article 4.3)

After the assessment of the fluoride removal treatment, the Commission will set the conditions of use of the treatment according to the provisions of Article 4.1(c) of Directive 80/777/EEC.

TERMS OF REFERENCE

In accordance with Article 29 (1) (a) of the Regulation (EC) no 178/2002 of the European Parliament and of the Council, the European Commission requests the European Food Safety Authority to examine the food safety aspects of the use of the activated alumina treatment for the removal of fluoride from natural mineral waters.

ASSESSMENT

To remove fluoride, the water is filtered through a bed of granulated activated alumina. The emphasis in this opinion is placed on the food safety aspects, in respect to the release of substances from the activated alumina and microbiological contamination of the NMW from the use of the filter. A report [5] was provided by the ad hoc working group4 on the technological assessment of natural mineral water treatments on the basis of dossiers [1-4] forwarded  to  the  Commission  by  the  industry,  national  food  safety  agencies  and specialised laboratories in water treatment. This information [1-5] was evaluated and is summarised below.

The Panel noted that filtration through a bed of activated alumina is legally used for many years in the production of drinking water in various Member States.

Activated Alumina

Activated alumina is a filter media made by treating aluminum ore (bauxite) so that it becomes porous and highly adsorptive. It consists mainly of Al2O3. The production process includes calcination at 500°C, which at the same time removes all organic substances. Besides the main components some trace elements may be present and the composition of the activated alumina may vary depending on the source of bauxite. To ensure that no impurities are released to the water during the treatment, the media used shall be tested according to the standard applicable for leaching tests (EN 12902) [6].

In any case the release of impurities during the treatment from the activated alumina into the NMW shall not result in concentrations exceeding the limits set in Commission Directive 2003/40/EC [7] or in the absence of limits in that Directive the restrictions set in Council Directive 98/83/EC of 3 November 1998 on the quality of water intended for human consumption [8] or in national applicable legislation.

Activated alumina is capable of removing a variety of substances including excessive fluoride, arsenic and selenium. The fluoride removal process is based on adsorption on the surface of the activated alumina. Before using the calcinated activated alumina for NMW treatment, an initialisation process is applied. During this process any impurities are removed from the media or decreased to a level that leaching of trace elements does not occur. Leaching of the main component, aluminium, depends on the pH and composition of the treated water. Besides the initialisation procedure, the activated alumina requires a periodic cleaning with an appropriate regenerating agent in order to remove absorbed substances and to restore the absorption capacity (see section 3.2).

Initialisation and regeneration procedures

Once a filter has been loaded with virgin activated alumina, the medium is backwashed to remove the fine particles generated by the handling of the material and subsequently chemically treated to activate the adsorption sites and to remove the impurities. The modalities of this treatment are similar to those for regeneration.

The regeneration of activated alumina filters is done in three stages:

•  Treatment  with  sodium  hydroxide  to  remove  fluoride  ions  and  replace  them  with hydroxide ions;
•   Treatment with an acid to remove residual sodium hydroxide and activate the medium;
•   Rinsing with drinking or demineralised water and conditioning with the natural mineral water so that the filter has no impact on the overall mineral content of the treated water.

The regeneration and in particular the first stage is also important from a microbiological point of view. During this stage, the pH of the water is ≥13. At this high pH, the solution is  bactericidal.  Biofilms  are  destroyed,  and  then  removed  through  subsequent  rinsing.

Humic and fulvic acids are also eliminated, thus preventing these compounds from building up over time.

Regeneration is carried out at intervals ranging from one to four weeks depending on water quality and throughput.

The reagents used for initialisation and regeneration have to comply with the relevant European standards relating to the purity of the chemical reagents used for drinking water treatment.

Fluoride and trace elements removal

It was demonstrated that fluoride can be removed effectively from natural mineral water by filtration through a bed of activated alumina using optimised conditions. To maintain the fluoride content of the treated water in compliance with the limits set in Directive 2003/40/EC, the fluoride content of the treated water needs to be monitored due to the reducing absorption capacity of the activated alumina during the cycle of use and regeneration.

When applying the fluoride removal treatment with activated alumina, the operating conditions may also lead to the co-removal of other undesirable constituents which are present in very low quantities (trace elements).

Release of substances by the use of activated alumina

Data on the actual content of many anions and cations in various types of NMW were provided. An increase of the concentration after the treatment was found in some cases for aluminium (from 18 up to 86 microg/l, bromide (160 -> 280 microg/l) and boron (66 -> 550 microg/l). However, in most types of water these changes were not observed at all and the observed variations of composition before and after treatment were low.

Leaching of aluminium from the activated alumina depends on the pH of the NMW and the alumina manufacturing process [5]. In some cases levels between 100 and 200 microg/l were reported. However, based on data provided [5] by optimising the pH conditions and selection of the appropriate medium the aluminium release resulting from the process would normally not exceed 40-60 µg/l.

Microbiological risks

Although NMW sources must be protected from microbiological contamination, they may contain bacteria naturally present at the source. Activated alumina, being a porous medium may be colonised with bacteria, with the formation of a biofilm. Periodical regeneration of the activated alumina at a pH of ≥13 is bactericidal and biofilms are destroyed and removed upon rinsing. Therefore it is concluded that with correct control of the process there is no additional risk of microbiological contamination.

Monitoring and control

The release of aluminium and other contaminants originating from the fluoride removal process should comply with the requirements of Directive 2003/40/EC [7] and in  the absence of requirements, with Council Directive 98/83/EC [8] and/or national applicable requirements and shall be checked regularly in accordance with the Council Directive. The fluoride content should be monitored frequently, preferably by on line measurements.

A process subject to GMP principles and a HACCP system should be implemented as required by the Regulation (EC) n° 852/2004.

DISCUSSION AND CONCLUSIONS

It was demonstrated that the treatment of NMW with activated alumina is suitable for the intended purpose. Under optimized conditions the release of cations or anions from the medium during treatment is negligible and will not pose a risk to human health. The total amount of aluminium ions in the NMW as it results after the release of aluminium from activated alumina should not exceed 200 microg/l, as established for drinking water [8].

The Panel notes that Joint FAO/WHO Experts Committee on Food Additives (JECFA, 2006) has recently adopted a new PTWI of 1 mg/kg bw (FAO/WHO, 2006).  If  it  is assumed that aluminium might be present in treated NMW up to 200 microg/l and 2 l of NMW are consumed daily, then aluminium intake from NMW would contribute at most up to 5% of the PTWI.

Due to the regular regeneration process of the activated alumina no microbiological contamination from the use of the filter is likely to occur.

Therefore it is concluded that the fluoride removal from NMW by means of filtration through activated alumina does not pose a risk to human health.

To ensure the above conclusions the following should be fulfilled:

•  The activated alumina should not release any significant amount of impurities. In any case the leaching of impurities and aluminium from the activated alumina into the NMW will not result in concentrations exceeding the limits set in Commission Directive 2003/40/EC [7], or in the absence of limits in that  Directive,  the restrictions set in Council Directive 98/83/EC [8] or in national applicable legislation.
•   Activated alumina is subject to an initialisation procedure before producing the treated NMW. The initialisation procedure includes the chemical treatment of the activated alumina to remove leachable impurities and a backwash treatment to remove fine particles.
•    Regeneration, using appropriate chemical treatment, is performed to remove the absorbed fluoride ions and to re-activate the active sites of the medium. In addition any biofilm possibly formed is also removed during this treatment.
•   The activated alumina used for treatment  of  NMWs  has  to  comply  with  the standard applicable for leaching tests (EN 12902).
•   The process should be subject to GMP and HACCP principles.

LIMITATION IN THE SCOPE OF THIS EVALUATION

This evaluation and opinion is based on an assessment of the treatment of NMWs for the removal of fluoride from these waters. It does not take into account any other treatment of NMWs.

DOCUMENTS PROVIDED TO EFSA

1. Application for permission to defluoridate natural mineral waters forwarded by the Belgian Federation of the Water and Soft drink Industry (FIEB).

1. “Reduction of Fluoride from natural mineral waters” forwarded by the German mineral water industry (V.D.M.).

1. “Etude des procédés de traitement pour éliminer le fluor applicables aux eaux minérales naturelles et aux eaux de source” forwarded by the French mineral water industry.

1. “Fluorid-reduktion bei Naturlichen Mineralwassern” forwarded by the German mineral water industry (V.D.M.).

1. Report of the Commission ad hoc working group5 on the technological assessment of natural mineral water treatments on the evaluation of treatment by aluminium oxide for the removal of fluoride from natural mineral waters and spring waters, dated 30-03-2006: http://ec.europa.eu/food/food/labellingnutrition/water/index_en.htm

1. European Standard EN 12902 of November 2004: Products used for treatment of water intended for human consumption. Inorganic supporting  and  filtering materials.

1. Commission Directive 2003/40/EC of 16  May  2003  establishing  the  list, concentration limits and labelling requirements  for  the  constituents  of  natural mineral waters and the conditions for using ozone-enriched air for the treatment of natural mineral waters and spring waters.

1. Council Directive 98/83/EC of 3 November 1998 on the quality of water intended for human consumption, OJ L 330, 5.12.1998, p. 32.

REFERENCES

JECFA (2006), the Joint FAO/WHO Expert Committee on Food Additives, sixty-seventh meeting, 20-29 Rome 2006, summary and conclusions: http://www.who.int/ipcs/food/jecfa/summaries/summary67.pdf

Discovering the Leaks
Mark Patience, product manager for water loss management line at Itron, says that he’s seeing a growing number—though not all—of municipalities investing more dollars into detecting leaks in their water delivery systems.

Patience says that many municipalities are even asking for leak detection capabilities to be included in the automatic meter reading/advanced metering infrastructure systems to which they are now upgrading.

This varies by state, though, with municipalities in some states particularly aggressive in tracking down and eliminating what the American Water Works Association refers to as non-revenue water.

Patience points to Tennessee, a state that he cites as enforcing especially stringent rules on how utilities can report non-revenue water numbers. “If officials in Tennessee see something that doesn’t make sense, they’ll perform an audit themselves,” he says. “That is kind of historic.”

Much of the increased attention to leaks and water management can be traced to the hot weather that has blanketed sizable portions of the United States in recent years. Many states in the southern portion of the country are struggling with drought conditions, Patience says. Some states, such as California, are trucking in water to their municipalities because they don’t have enough.

“Many utilities are not able to meet the demand of their users,” says Patience. “These utilities have to put more effort into preventing water from escaping from their systems.”

Other municipalities want to prevent the future, often more costly, problems that can result when leaks are not identified and repaired, says Wilson.

Leaks can be devastating if left untreated, he says. They could steadily increase the amount of water that flows into a municipality’s wastewater treatment plant, eventually overwhelming the facility. They could push chlorinated water into a nearby creek. They could even undermine the stability of an entire street, leading to a costly cave-in.

“Leaks can cause a whole dimension of collateral damage if they are not repaired,” says Wilson. “We’ve all seen pictures of fire trucks falling into holes in the street. We’ve all seen giant sinkholes in busy intersections. Often that was caused by leakage. And it’s not often caused by a big break, but by leakage over time. It builds up.”

The cost of the collateral damage, then, is often much higher than losses utilities experience from non-revenue water, Wilson says. “These are the losses that utilities need to consider when they wonder whether to fix a leak or to invest in leak detection,” he says. “The actual financial losses from water loss might not seem so bad. But when you consider the long-term damage that leaks can cause, that changes the financial situation.”

Even with collateral damage factored in, though, not all municipalities are as careful as others when it comes to detecting leaks and performing water audits.

Again, Patience points to outside factors for an explanation.

While many parts of the country are fighting through drought conditions, many other municipalities sit in parts of the United States where water is not only plentiful but cheap, too. If water is cheap enough, it’s not cost-effective for these utilities to invest in leak detection. Simply put, the technology is too expensive and the cost of water too cheap to make advanced leak detection a worthwhile investment for such utilities.

Today, many utilities are strapped for both cash and manpower. State budgets remain squeezed throughout the country. And municipalities facing budget hurdles aren’t likely to hire the staffers necessary to conduct water audits and monitor leak detection if the cost of water isn’t high enough to justify the extra expenditures, Patience says.

“Some utilities barely have enough staffers to go out and read the meters,” he adds. “They’ll outsource that work to third-party contractors. These utilities aren’t likely to hire the manpower needed to accurately track non-revenue water.”

Utilities face another hurdle when it comes to water audits and leak detection: the knowledge gap.

Doug McCall, director of marketing for Sensus, says that many utility managers have no real idea of how much water that’s escaping from their treatment and delivery systems each month.

Such utilities don’t have the technology they need to tell them how much water they’re pumping into the ground, McCall says. “A lot of utilities will tell you that they think they’re losing about 10% of their water in leaks,” he adds. “That’s actually pretty low. Best-in-class standards are 7%. But when you dig into the utilities’ data, you’ll find that they are just estimating how much water they are losing. There are political and other reasons why utilities want to keep that number low. If you do a real system test, you’ll find that most utilities are losing from 15 to 25% of their water. That is the range that we usually find.”

And once utilities are armed with this knowledge? They’re generally more likely to take steps to address their high percentage of non-revenue water.

The good news is that leak detection technology has improved over the years. Today, it can far more accurately tell utilities exactly how much of their water isn’t being delivered to their customers.

Sensus provides a good example. Sensus engineers can study the entire water infrastructure of a utility to determine how much water a utility is pumping into its distribution network and how much actually comes out of it.

It sounds like simple math. But it’s more complicated. By measuring water flow at meters located throughout the distribution system, and subtracting out the flow through utilities’ service connections, Sensus can calculate how much water these utilities are pumping into the ground instead of delivering to their customers.

There are complications, though. For instance, some utilities don’t meter parks or other public services, McCall says. Still, a macro approach can give utilities a solid feel for how much non-revenue water they are generating.

Sensus also works with partners that provide acoustic technology that lets engineers listen to pipes to find the biggest leaks in a system. Sensus will often deploy these partners after performing a macro analysis of a utility’s water distribution system.

Once Sensus identifies the zones that are plagued by the most leaks, the company’s partners will analyze these sections with acoustic technology to pinpoint specific leaks. Armed with this knowledge, utilities can then dispatch crews to exact locations to fix these potentially costly leaks. “If you own a water utility with a dozen zones, we can do an analysis on each zone,” says McCall. “We can tell you which are the top zones that are leaking the most water on a macro level. This is helpful information. We can then take acoustic technology to find the biggest leaks. This is a powerful combination of two different technologies that can help utilities cut down on their leaks.”

Sensus offers technology that directly benefits property owners, too. The company, for instance, offers meters that can identify continuous flows of water to residences or commercial properties. If the meters detect a continuous flow for more than 24 hours, the utility is notified of a possible leak. Utility crews can then investigate and, hopefully, repair a leak before too much water is lost.

Changing Attitudes
Improved technology, though, hasn’t converted all utilities to fans of water audits and leak detection . . . yet.

Craig Hannah, development manager with Johnson Controls, says that the majority of utilities across the country still don’t view leak detection and water audits as anything close to a priority.

But he also says that this is slowly changing.

Part of the reason? The cost of water.

The cost of water has been relatively inexpensive for decades, Hannah says. But as municipalities look to the future, they realize that this will likely change. Water prices won’t decrease, but they might very well rise, Hannah says.

And because of this, utilities will be encouraged to take more steps to monitor exactly where their water is going. This will include both leak detection and a greater number of utilities ordering regular water audits, he says.

“Attitudes are slowly changing. For the longest time, people have viewed water distribution as a service, just like police and fire protection,” says Hannah. “No one questions the need to provide police and fire protection, just like no one questions the need to provide clean drinking water. But as long as municipalities treat water as a service, and not as a business, they won’t worry as much about the water they are losing from their system.”

McCall from Sensus agrees. “The primary goal in life of a utility is to make sure that clean, potable water comes out of the taps when customers turn them on,” he says. “If utilities pump some of that into the ground, even if it’s 15%, 20%, or 25%, as long as the utility is delivering clean water, no one’s that worried.”

This is changing, though. Many state legislatures—Texas and Tennessee among them—have mandated that utilities must conduct regular water audits as a way to prevent large water losses. Such requirements have become more frequent as water becomes both scarcer and, at least slightly, more expensive.

“The factors are lining up for some changes in the way utilities treat non-revenue water,” says Hannah. “The cost of water has been so low for so long, I really can’t imagine that cost decreasing any time in the future. If anything, it will rise. At the same time, the technology for monitoring water is improving. That’s a combination that is making an impact.”

In addition to price and legislation, another factor is motivating utilities to focus more heavily on leak detection and water monitoring: customer service.

Utilities that want to provide the best customer service need to invest in leak detection. Customers will appreciate it when their utility proactively takes step to stop leaks at their homes and businesses before they develop into more costly problems.

Sensus software, for instance, can alert utilities to potential leaks in the system. Sensus also provides software that notifies the end users of water that there is a potential problem. These notices can come in a number of different ways, including e-mail messages and text alerts.

“We can send a sudden-flow alert,” says McCall. “We can tell end users that something is broken.”

Other utilities are relying on out-of-town notification systems to provide better service to their customers. Such systems allow homeowners or business owners to notify their utilities by e-mail that they will be out of town for a certain number of days. If the utility sees water use at these properties, it can alert their owners that there might be a potential leak. If the water use meets or exceeds certain thresholds, the utility can send crews to investigate.

Detecting Leaks in Clayton County
The Clayton County Water Authority in Morrow, GA, provides water to more than 75,000 customers. The authority has five raw water reservoirs and can produce up to 42 million gallons each day of potable water.

Staffers here also maintain about 1,500 miles of water distribution pipes, 1,400 miles of sewer conveyance pipes, and 500 miles of stormwater infrastructure.

The water authority is also committed to reducing its non-revenue water.

In 2000, the authority began working with Itron to detect its leaks. This decision came after Clayton County at the start of that year found that its non-revenue water losses were nearing an unsustainable 20%.

 More About UV

The clean, classic Watts UV unit. A powerful and effective but simple system that makes non-potable water safe to drink. It is rated for 30mJ/cm2 at the specified flow rate.

Disinfection chemicals like chlorine are measured in “parts per million” of the disinfectant.  Straining devices are measured by the micron size of the filter.  UV is a little more complicated.  The standard measure of UV dosage is mJ/cm²,  millijoules per square centimeter.  This number is a measurement of the intensity of the lamp with consideration of how fast the water flows past the lamp. Although NSF standard is 40mJ/cm², in the water treatment industry it is generally assumed that 30mJ/cm² is more than enough to treat residential well water.  In fact, a 16mJ/cm² unit is twice as hot as it needs to be.  6-10mJ/cm² is sufficient for most pathogens.  6mJ/cm² will do away with 99.99 percent of E. coli.

As ProPublica has reported in an ongoing investigation about America’s management of its underground water, the U.S. Environmental Protection Agency has issued more than 1,500 permits for companies to pollute such aquifers in some of the driest regions. Frequently, the reason was that the water lies too deep to be worth protecting.

But Mexico City’s plans to tap its newly discovered aquifer suggest that America is poisoning wells it might need in the future.

Indeed, by the standard often applied in the U.S., American regulators could have allowed companies to pump pollutants into the aquifer beneath Mexico City.

For example, in eastern Wyoming, an analysis showed that it would cost half a million dollars to construct a water well into deep, but high-quality aquifer reserves. That, plus an untested assumption that all the deep layers below it could only contain poor-quality water, led regulators to allow a uranium mine to inject more than 200,000 gallons of toxic and radioactive waste every day into the underground reservoirs.

But south of the border, worsening water shortages have forced authorities to look ever deeper for drinking water.

Today in Mexico City, the world’s third-largest metropolis, the depletion of shallow reservoirs is causing the ground to sink in, iconic buildings to teeter, and underground infrastructure to crumble. The discovery of the previously unmapped deep reservoir could mean that water won’t have to be rationed or piped into Mexico City from hundreds of miles away.

According to the Times report, Mexican authorities have already drilled an exploratory well into the aquifer and are working to determine the exact size of the reservoir. They are prepared to spend as much as $40 million to pump and treat the deeper water, which they say could supply some of Mexico City’s 20 million people for as long as a century.

Scientists point to what’s happening in Mexico City as a harbinger of a world in which people will pay more and dig deeper to tap reserves of the one natural resource human beings simply cannot survive without.

“Around the world people are increasingly doing things that 50 years ago nobody would have said they’d do,” said Mike Wireman, a hydrogeologist with the EPA who also works with the World Bank on global water supply issues.

Wireman points to new research in Europe finding water reservoirs several miles beneath the surface — far deeper than even the aquifer beneath Mexico City — and says U.S. policy has been slow to adapt to this new understanding.

“Depth in and of itself does not guarantee anything — it does not guarantee you won’t use it in the future, and it does not guarantee that that it is not” a source of drinking water, he said.

If Mexico City’s search for water seems extreme, it is not unusual. In aquifers Denver relies on, drinking water levels have dropped more than 300 feet. Texas rationed some water use last summer in the midst of a record-breaking drought. And Nevada — realizing that the water levels in one of the nation’s largest reservoirs may soon drop below the intake pipes — is building a drain hole to sap every last drop from the bottom.

“Water is limited, so they are really hustling to find other types of water,” said Mark Williams, a hydrologist at the University of Colorado at Boulder. “It’s kind of a grim future, there’s no two ways about it.”

In a parched world, Mexico City is sending a message: Deep, unknown potential sources of drinking water matter, and the U.S. pollutes them at its peril.

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Pro Publica original.