Untreated surface water in rivers, streams, lakes, and ponds is not safe to drink unless it is treated to remove bacteria, viruses, and parasites.
Drinking water contaminated by these organisms can cause diseases like cryptosporidium or giardia. Symptoms can include nausea, diarrhea, weight loss, gas, and energy loss.
Sources of Contamination
The quality of surface water is unpredictable, because the water continually moves and pollutants can be introduced at any time. In other words, an area of lake or stream that is fine one day may be contaminated the next.
Biological contaminants can come from sewers and failed septic systems, boat toilets, animals, and other sources.
Chemical contaminants, like gasoline, oil, pesticides, and heavy metals, can come from discharge pipes, chemical storage areas, gasoline tanks, oil drums, or anywhere chemicals have been used close to open water.
Location, Construction of Water Intake
To use surface water as a source for drinking water, you must have a properly constructed water intake and a treatment system that includes filtration and disinfection. (See Water Intake and Treatment System Diagram). Hire a qualified consultant to design the system.
Be aware of possible contamination sources, like barnyard runoff or discharge pipes, when locating the intake pipe. Place the pipe in the deepest, most remote ‘clean water’ possible. Avoid areas of high algae growth.
Treatment has two steps, filtration and disinfection. Both steps are necessary to remove or kill all bacteria, viruses, and parasites and make the water safe to drink.
Step 1. Filtration removes soil particles and plant material that can interfere with disinfection. It also removes parasites that are not killed by disinfection. A one-micron filter is required for complete removal, because some parasites can be as small as two microns.
- A single one-micron filter is likely to clog as it removes sediment and algae. As a result, home systems commonly use a series of cartridge filters, with each filter removing smaller particles.
- Another option is a rapid sand filter followed by two cartridge filters. These systems filter all the water entering a home.
- Some people treat only the kitchen tap water for drinking. An option in this case is to use reverse osmosis followed by ultraviolet light or a small distillation unit.
Step 2. Disinfection is needed because some bacteria and viruses can pass through filters.
Chlorination—When disinfecting using constant chlorination, a small pump automatically injects a diluted chlorine solution, usually household bleach mixed with water, into the water pipe below the filter. The chlorinated water then flows into a holding tank, where the chlorine kills any organisms. This disinfects the entire home plumbing system. Constant chlorination systems require some maintenance by the owner.
The amount of chlorine needed to kill harmful organisms depends on the temperature and acidity of the water and the length of time the organisms are in contact with the chlorine. Consult a water treatment specialist or engineer for specific assistance.
Chlorination may form by-products called trihalomethanes (THMs), some of which pose a slight cancer risk after prolonged consumption. An activated carbon filter can be used to remove THMs, along with the chlorine, taste and odor, and any other hazardous organic chemicals. Carbon filters must be changed periodically.
- Ultraviolet Light (UV)—In this type of disinfection, the filtered water enters a canister containing an ultraviolet light fixture. Ultraviolet radiation kills bacteria and viruses. This system does not produce THMs, nor does it disinfect the household plumbing. The ultraviolet lamp must be changed periodically.
- Warning—Be sure to boil for five minutes any untreated surface water used for drinking. This will kill any dangerous organisms in the water. Use only boiled water for brushing teeth; washing fruits and vegetables; and making ice cubes, juice or baby formula. Unboiled water can be used to wash dishes, as long as the dishes are allowed to air-dry before use.
- Plan to install a filtration and disinfection treatment system.