How do water companies filter and purify water for drinking?

[bluemoonKY]

I am curious as to how utility companies or water companies filter and purify water for drinking. Specifically, I am most curious as to how water companies filter and purify water for drinking that is taken from rivers. My hometown is Huntsville, AL, and Huntsville Utilities provides the drinking water in Huntsville. I know that Huntsville Utilities gets most of the water it provides for drinking from the Tennessee River. How do water companies typically filter out the debris that inevitably must come in with the river water? I suppose a water company could use giant metal screens to filter out things like twigs and tree branches, but how does the water company filter out things like grains of sand or other small particles. I know that the water companies use chlorine to purify water for drinking. Chlorine would probably kill all the microbes, but how do water companies remove chemical pollutants from drinking water?

 

[Evo]

It seems they say to contact them if you want information.

http://madisoncountyal.gov/about/org/CoDepts/WaterSource.pdf

 

[klimatos]

but how do water companies remove chemical pollutants from drinking water?

They generally don't bother, since it is both difficult and expensive. Back when I was a Director of Water Quality for a three-county planning district in Michigan, the story went around that the EPA announced that it had found 67 known carcinogens in the drinking water of Cincinnati. Scientists from the Cincinnati Water Board then went to the nearby EPA regional headquarters and found 72 known carcinogens in the drinking fountains there.

I find it very likely that both analyses were valid. Adding chlorine to drinking water produces dozens of carcinogens that were not there previously. The concentrations are minute, and the exposure a lot safer than the risk of cholera and typhus from untreated water.

 

[SteamKing]

About 30 years ago, there was a spill of phenol into the Mississippi River above New Orleans. The drinking water for the city and surrounding suburbs was taken directly from the river at several points. The advisory put out by the local utility companies stated that the water would have a chemical smell and taste for several days (which it did), but that no other ill effects from consumption were expected. When the spill passed the city, the taste and smell of the water returned to what it had been prior to the spill.

With a big river like the Mississippi, there is plenty of sediment suspended in the water, logs, dead bodies of animals (and sometimes people), fertilizers and other chemicals, so there is no way to remove all of this material and produce 100% pure water at a reasonable cost and in the quantities which a major metropolitan area consumes. You treat the water to remove disease carrying microbes, using chlorination and aeration, maybe let it filter through a large sand bed to remove the visible contaminants, and cross your fingers.

The attached article (or book as it is about 120 pages long) discusses the various methods used in Western Europe to treat and filter drinking water:

http://www.who.int/water_sanitation_health/publications/ssf9241540370.pdf

 

[LudusRex]

Water companies use a multi-step process to filter and purify water for drinking. The first step is typically a physical filtration process, where the raw water is passed through multiple layers of screens and filters to remove large debris such as twigs, leaves, and branches. This process is also known as screening or straining.

After the physical filtration, the water undergoes a chemical treatment process. This involves adding chemicals such as alum, which helps to coagulate and remove smaller particles like sand and sediment. The water is then sent to settling tanks, where the particles and chemicals settle to the bottom and are removed.

Next, the water is sent through a series of filters, typically made of sand, gravel, and activated carbon. These filters help to remove smaller particles and impurities from the water. Some water companies also use advanced filtration techniques such as membrane filtration, which uses a semi-permeable membrane to remove even smaller contaminants.

Once the water has been physically and chemically filtered, it is disinfected to kill any remaining microbes and bacteria. This is where chlorine is typically used. Other disinfection methods may include ozone, ultraviolet light, or chloramines.

To address chemical pollutants, water companies may also use additional treatment processes such as activated carbon adsorption, which helps to remove organic contaminants, and ion exchange, which removes dissolved metals and other chemicals.

It is important to note that the specific processes used by water companies may vary, depending on the source of the water and the level of contamination. However, the overall goal is to remove impurities and make the water safe for drinking. Regular testing and monitoring are also crucial to ensure the water meets all safety standards before it is distributed to consumers.