What Happens to Stagnant Water?
Under the Safe Drinking Water Act, water treatment plants must comply with National Primary Drinking Water Regulations (NPDWR). The NPDWR sets maximum contaminant levels and/or treatment techniques for over 90 contaminants, ensuring that water leaving the plant is safe to drink. To make sure your water remains safe to drink at point of use (i.e. faucet, water fountain, or shower), water treatment plants add additional disinfectants and corrosion inhibitors. There are a variety of options to choose from, which can be optimized for a particular system’s source water quality or distribution system. Despite these efforts, hazards may remain in your drinking water if it has been sitting in your pipes for an extended period of time. These hazards include: Legionella, disinfection byproducts, and lead/copper.
Legionella
After disinfectants are introduced into the water supply, they inactivate (or kill) germs and other bacteria. The longer the water remains in the pipes (“water age”), the less effective the disinfectants become. If the water age is too high, then biofilms can form on the inside of pipes. Biofilms are layers of potentially harmful germs and bacteria.
Legionella is a bacteria associated with biofilms, and causes Legionnaires’ disease, a serious type of pneumonia. The longer water sits in pipes, the greater the chance that Legionella can grow and spread. Luckily, this is only a concern when water is stagnant for prolonged periods of time, on the order of weeks or months. Typical day-to-day use will cycle enough tap water through your pipes to keep the water age low enough to retain disinfection capacity and mitigate risks associated with Legionella.
Disinfection byproducts
Common disinfectants used in drinking water treatment systems include chloride, chloramine, chlorine dioxide, ultraviolet light (UV), and ozone. Disinfectants differ between various plants, optimized based on a range of factors including source water quality and distribution system. As discussed previously, the effectiveness of these disinfectants decreases with water age. Another risk associated with increased residence time (the length of time water remains in the pipes before reaching the tap) is disinfection byproducts. Chlorine and chloride dioxide are highly effective at inactivating germs and bacteria, but can form toxic byproducts such as trihalomethanes, haloacetic acids, and chlorite. These compounds are also regulated by the NPDWR and commonly monitored to ensure public safety.
Lead and Copper
Lead and copper are key contaminants of concern due to their prevalence in our water supply and their drastic health effects (see Effects of lead in drinking water). National efforts have been made to reduce exposure, namely lead service line replacement, but that remains only part of the problem. Indeed, lead and copper can leach into your water supply from lead pipes (see How does lead get into tap water?), but internal plumbing may also introduce metals into your water (see lead service lines). Compared to disinfection byproducts and Legionella, lead and copper can enter your water on a much shorter time-scales, on the order of hours to days.
Solution
There are a range of methods to reduce these hazards (see Filters vs. Auto-flushing), but the most comprehensive remains flushing your pipes. Recommended by the City of Chicago’s Department of Water Management (DWM), daily flushing is the easiest way to promote water quality at home. The DWM suggests flushing water for 5 mins after it has been sitting for 6 or more hours to reduce water age. A lower water age ensures that disinfectants are able to inactivate germs and bacteria, disinfection byproducts aren’t able to form, and lead/copper aren’t able to leach into the water supply.
Manual flushing can be tedious, since it needs to be done consistently to be effective. Noah System has developed a solution, auto-flushing. Auto-flushing automatically runs water through your pipes at predetermined intervals to maintain water quality without you thinking about it. The system has already been effectively implemented in Chicago Public Schools (CPS) to reduce lead risks in drinking fountains and promote public health. Learn more at Noah System.
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