Rainwater Falls from the Sky, But It Must Be Purified For Drinking

As water becomes scarce, rainwater collection systems are becoming increasingly popular.

After water is collected and stored for later use, water treatment is essential. This usually takes the form of filtering out large particles then treating for microbiological safety. If the water is contaminated with chemicals from its collection process (for example, roofing materials if the water is collected from a roof), then a good carbon filter should be added to the treatment.

Filtering for sediment can be either with cartridge filters or, if there is a lot to be filtered out, a backwashing filter that filters down to 10 microns or so.

After elementary filtration to remove particulate, it is critical that some form of disinfection be used. This can be:

Chlorination, the old standby, followed by carbon filtration to remove the chlorine.

Ultraviolet (UV), which is probably the most popular single rainwater treatment. The water must be very clean when it passes the UV lamp to assure complete disinfection. UV has the advantage of adding no chemicals to the water. It should be the last stage in the treatment process.

Ozonation is an excellent disinfectant, but is a bit more challenging for the homeowner from the technical viewpoint.

Ultrafiltration (UF) is gaining popularity in rainwater treatment. UF filters down to about 0.02 microns—enough to remove cysts, bacteria and viruses. Again, water must be pre-filtered before the UF membrane to protect it from premature clogging of the ultrafiltration equipment.

Rainwater, with only the minimal treatment described above, can provide extremely good water. Its mineral content (TDS: Total Dissolved Solids) is very similar to that of reverse osmosis water.

Reference Source:  The Pure Water Occasional.