The U.S. Environmental Protection Agency’s (EPA) Water Infrastructure Resiliency and Finance Center, in collaboration with the...
Choosing the right treatment option for the water supply
Over the years, the public has become more aware of drinking water quality issues. Urban development has placed increased stress on water resources, which in turn has increased the need for cost-effective methods to treat drinking water. This is true regardless of whether the installation is at a single point of use (POU) or at the point of entry (POE) for treating all water used in the home.
At the POU level, a water treatment system only affects one faucet or water access point. For POU applications, reverse osmosis (RO) is a popular choice since it can provide chlorine and sediment removal as well as reduction of dissolved contaminants (e.g., heavy metals) in one unit. However, the benefits of low cost and minimal maintenance should be balanced against significant water wastage to the drain.
In some applications, a single inline filter is sufficient for taste, odor and sediment reduction. If only a single filter is supplied for drinking water, it is recommended that the water be free of pathogens such as bacteria, viruses and parasitic cysts. In conjunction with a pretreatment system, a properly installed ultraviolet (UV) disinfection system can ensure drinking water is microbiologically safe. Treating water at the POU level can be simple and cost-effective in certain situations, especially those involving low volumes of water and minimal plumbing requirements.
For bacteriologically unsafe water, there is a growing demand for UV treatment. Historically, chemical treatment using chlorine was the primary method of disinfection, but the growing awareness of disinfection byproducts and their associated potential health concerns, in addition to the unnatural taste and odor that can result from chlorine use, have allowed other technologies to enter the market.
One benefit of UV treatment technology is that it does not modify or add anything to the water, while still providing disinfection when harmful bacteria, viruses and cysts, such as Cryptosporidium and Giardia, are of concern. UV technology is cost-effective and simple in its functionality. Water flows through a reaction chamber and is exposed to a specific wavelength of UV light (254 nanometers), which disrupts microorganisms’ DNA, preventing reproduction. The reproduction of microorganisms inside the human body leads to illness and is the mechanism that produces a positive bacteria test, or colony count. For optimal UV treatment, the appropriate pretreatment must be put in place to ensure adequate UV light transmission through the water. The recommended minimum pretreatment is filtration down to 5 microns, which can be achieved with a high-quality sediment prefilter.
When dealing with surface water or shallow wells, a UV system equipped with a sensor is recommended, as water quality can change quickly based on dry conditions or heavy rains. These water sources may contain variable levels of tannin, a slight coloration caused by decomposed vegetation that can reduce UV transmission levels, requiring specialized tannin removal pretreatment. Water quality in a drilled well can change over longer periods of time, but typically remains consistent with proper levels of UV transmission.