And why you may still need a home filtration system when your local treatment plant is very good at filtering your water |
 A water treatment plant designed to improve the quality of a contaminated drinking water before it's distributed to homes. A public treatment system consists of preliminary screening, coagulation, sedimentation, filtration, and disinfection. Some water treatment plant may require addition treatment steps like aeration, ion exchange, or distillation.
Sources of water for treatment include lakes, streams, rivers, and groundwater. Since raw water from these sources are most often unhealthy to drink, a treatment plant is necessary to remove any dangerous chemical and biological materials as required under the USEPA Safe Drinking Water Act. Sources of water contaminattion: Human activities: - Street litters
- Failed septic systems
- Sanitary sewer overflows
- Combined sewer overflows
- Agricultural runoffs
Natural activities: - Dissolved organics from rocks, and dirty rain.
- Harmful bacteria from wildlife and soil.
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Stages of Water Treatment |
 | Preliminary Screening
Screening is necessary to remove floating debris from the source water such as dead woods, leaves, rags, or from runoffs from storm events or snow melts. Some screening could be very fine screen materials or micro-strainers to remove suspended algae and plankton.
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 | Coagulation
Coagulation process is to remove dirt and other suspended particles missed by screening through the addition of alum and other chemicals. These contaminants flow toward the chemicals to form "flocs" which attract other impurities. The flocs become heavy and are separated from the water through the next process - sedimentation.
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 | Sedimentation
Water is allowed to sit in a tank for a pre-designed number of hours allowing flocs and other heavy materials to settle at the bottom of the tank—which looks like a giant swimming pool. The combination of alum from the coagulation step and contaminants will settle at the bottom leaving the clear water on the surface. The bottom solids (sludge) is pumped out, treated, and properly disposed of.
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| Filtration
This process involves passing water through filters which could be layers of sand, gravel, and charcoal that help remove even smaller particles. Other filtration systems may include packaged filtration, membrane filtration, and diatomaceous earth filtration. The ultimate result is to filter out any particles that remain unsettled during coagulation and sedimentation processes.
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Disinfection
Disinfection is the most important part of water treatment which is the process to kill or inactivate any pathogenic bacterial in the source water. Methods of disinfection include chlorination, chloramines, ozone, ultraviolet light, and nanofiltration.
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 | Storage
Storage tank is very important. It allows water to be distributed to homes with enough pressure during power outages. Because of their high elevation, storage tanks allows water to flow with reliable pressure to flat areas.
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Why do you still need to buy a home water filter?
Water that won the best tasting award can still be unhealthy to drink inside you home because of contamination after it has gone through the elaborate treatment. The following are a few of the reasons why you may still need to filter your water regardless of the treatment steps: - Chorine residual from disinfection step may cause itchiness and dry skin after shower for most people. Some people may be allergic to the residual chlorine smell and taste. So, a shower filter or a whole house water filter may be necessary to reduce this unpleasant chemical.
- Lead in old pipes or in solders may leach into water inside the home requiring a filter designed to effectively remove lead in water.
- Bacterial regrowth is a common phenomenon where bacteria that grow within distribution pipes can contaminate the water that has gone through treatment.
- Water in storage reservoirs could be contaminated when exposed to fallout dust and dirty air. Birds and rodents may may contaminate water with excrement if they gain access through vent openings in a closed or defective water tanks.
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