Have you ever given any thought to the process that makes the water you drink from your tap drinkable? No? You're not alone. Most of us don't; we simply expect that when we turn on the tap in our kitchens and bathrooms the water will be clean and will pose no harm to our health.
The process it undergoes between the source and the end of the distribution line depends on the source of the water. Water sourced from lakes will require a different form of treatment than water from an underground aquifer, a river or the sea.
Water treatment processes can be broken down into three categories; physical processes like filtration, biological processes like sand filters and chemical processes such as chlorination. Again the source of the water will determine which process, or combination of processes, is required to produce potable, or drinkable, water.
Surface water for example, is commonly pre-treated by screening, which is a physical process. Screening removes large particles like sticks and branches, leaves and garbage from the water before it is stored. Groundwater from an aquifer is usually not screened since Mother Nature has done that job already.
Source water that is rich in minerals may be pre-treated with soda ash (sodium bicarbonate). This is called preconditioning. Municipalities may also add chlorine to the water to prevent the buildup of organism that could contaminate the pipes and the storage tanks. Both of these are chemical processes.
Often the PH level of the source water will need to be adjusted so that subsequent processes work more effectively. If the PH level of the source water is alkaline (PH level above 7, which is neutral), hydrogen chloride (HCl) or carbon dioxide (CO2) can be used to lower the PH level. On the other hand, water which is alkaline (PH level below 7) may be treated with lime to raise the PH level.
Next comes a process called flocculation, which, simply put, clarifies the water. Flocculation ensures that the water becomes clear and without color. Coagulants such as iron hydroxide, aluminum hydroxide or a synthetic polymer, are added to the water. Small particles in the water attach themselves to the coagulants. The water is gently stirred, and the particles, called precipitate, grow larger as more suspended particles in the water are picked up. The water is then filtered, often through a coarse sand filter.
The next step is usually sedimentation. The water is slowly moved into a large basin where particles not removed by the sand filter settle to the bottom of the basin. This process is also called clarification.
Then comes filtration. There are several different types of filtration used, depending on requirements. The most common filtration medium is sand, above which is a layer of activated carbon or anthracite. Other mediums include lava filters which incorporate water purifying plants and synthetic membranes.
The last step is disinfection to kill any viruses and bacteria. Most municipalities must also ensure that there remains enough disinfectant in the water as it passes through the distribution channel and into your home. Disinfection may include the addition of chlorine, chlorine dioxide, ozone and hydrogen peroxide.
What I've described above is a simplified version of municipal water purification. Each municipality has to determine the best, not to mention the most cost effective, methods to ensure compliance with local, state/provincial and federal regulations.
If you're interested in learning more about your local water treatment facility, don't hesitate to give them a call. Most have regularly scheduled public tours, and if they don't, ask for one.
