When you flush your toilet or run water down a drain, where does it go? Most people are vaguely aware that there are municipal water treatment systems in their community, but they don't know what processes the wastewater is put through in order to purify it. Industrial, business, and residential liquid wastes all run down sewers which then route them to facilities where they are cleaned up and made ready for use again. After all, we don't have enough water resources on the planet to be able to afford to dispose of water without cleaning it and reusing it. That's the purpose of municipal water filtration.
Our sewer systems consist of pipes and pump stations that move the wastewater to the treatment facility. Many municipal water treatment systems use a 3-stage process. In the primary stage, sewage is kept in tanks where the heavy solids are allowed to sink to the bottom. This also allows the lighter materials, such as grease and oil, to rise to the top. After removing all the solids that have accumulated in the bottom of the tank as well as the lighter ones on top, the water is ready to be sent on to the second step of the process.
The second treatment the wastewater goes through takes out all of the biological matter that's either suspended or dissolved in it. At this phase indigenous organisms, those that come into the water naturally without any human input, are introduced into the wastewater, because they clean up the harmful organisms and matter. After they have done their job, it's often necessary to do a separate treatment in order to remove them from the water, too.
The final phase, known as tertiary treatment, is anything that needs to be taken care of that's on and beyond what the first two treatments removed. Sometimes water is disinfected using chemicals, and other times physical disinfection methods are used, such as microfiltration and lagoons. Once the water has come through all of the municipal water treatment systems, it is safe to be discharged into a river, wetland, stream, lagoon, or bay. In many cities it is used to irrigate golf courses. Water that is really clean may also be used to recharge groundwater or in agriculture.
As you can see, municipal water filtration is a lengthy and expensive procedure; however, it is very necessary. In some foreign countries, people actually make their waste right in the water sources, and that leads to disease epidemics and death. Therefore, it's important that our tax dollars be used to maintain our water treatment systems.