Acidic Water

by Pure Water Annie

 Gazette technical wizard Pure Water Annie offers a nutshell view of treating acid water.

Acidic water is, by definition, any water with a pH of less than 7.0.

Water that is low in pH can have undesirable effects on plumbing fixtures and piping. Green staining of fixtures is a common indication of acidic water. Copper pipe can be ruined by water low in pH.

Low pH is also an issue in water treatment. Sometimes it is necessary to raise the pH of acidic water in order for other treatment strategies to apply. For example, oxidizing iron to prepare it for filtration is difficult if the pH of the water is low, so raising the pH of the water is often the first step in removing iron from well water.

Almost all water treatment issues involve pH in some way. Water constituents change in nature as pH changes, so many treatments can be applied only if pH is within the desired range.

Although the sales strategy of a class of drinking water products called “ionizers” is based on raising the pH of acidic water, there is no evidence that drinking water low in pH has any negative effect on health. Taste, of course, can be an issue if the pH is very low.

Treating Acidic Water

The pH value of water decreases as the amount of carbon dioxide, CO2, increases, and pH increases as the amount of bicarbonate alkalinity increases. The ratio of carbon dioxide and bicarbonate alkalinity within the ranges of 3.6 to 8.4 is an indication of the pH value of the water.

Acidic water can be corrected by several water treatment strategies. A common treatment is injection of soda ash, and a more aggressive treatment is the injection of caustic soda (sodium hydroxide). This is usually accomplished by injecting a solution of the soda ash or caustic soda directly into the water pipe.

A second strategy is to run the water through a bed of calcite (the most common treatment mineral) or corosex. As the low pH water passes through the bed, the mineral dissolves into the water and raises its pH.

Calcite treatment raises the pH by adding calcium carbonate to the water. This has the sometimes undesirable effect of increasing the hardness of the water slightly. Calcite and corosex are most commonly used in backwashing filters, but calcite alone can be used with simple upflow filters if the water is reasonably clean. Calcite is also commonly used in cartridge form as a postfiltration treatment for undersink reverse osmosis units. RO lowers pH, and calcite filters are used to bring the pH back to neutral.

Go here for more information about calcite filters or soda ash feeders.

Also, more about pH and water.