Monday, March 30, 2015

The Smell of Chlorine Means It’s Spring

You may notice a slight chlorine taste and smell in your drinking water during over the next few weeks. Fairfax (and Arlington) have started their spring flushing program for their water systems. This is not harmful, but is important step to remove residue from the water distribution system. Flushing the water system entails sending a rapid flow of chlorinated water through the water mains. As part of the flushing program, fire hydrants are checked and operated in a coordinated pattern to help ensure their operation and flushing of the system.

Flushing of the water distribution system removes sediments comprised mostly of minerals which have accumulated over time in the pipes. An annual flushing program helps to keep fresh and clear water throughout the distribution system. Removing the residue ensures that when the water arrives in your home, it is the same high quality as when it left the water treatment plant. Though you might detect the slight chlorine smell or taste, this is not harmful and the water remains safe to drink. If you are a coffee and tea lover like me, use filtered water or leaving an open container of water in the refrigerator for a couple of hours to allow the smell to dissipate

Drinking water in Fairfax (and over 94% of local public water supply) comes from either the Potomac River or Occoquan Reservoir. This water needs to be treated to remove impurities and disinfected to kill disease causing germs such as Salmonella, Campylobacter, and norovirus. Giant screens on the water intake pipes prevent trash, debris and fish, but the water is only screened and not yet drinkable. In the water treatment plant potassium permanganate (KMnO4) is added to the water to control taste and odors, remove color, prevent biological growth within the water treatment plant, and remove iron and manganese which are naturally occurring predominantly nuisance contaminats.

Then water is pumped into a series of water chambers where the pH is adjusted by adding either caustic soda or sulfuric acid and a coagulant to remove small particles of dirt suspended in the water. The water moves through a series of mixing chambers with progressively slower mixing to allow the particles to coagulate into larger and larger particles until dirt floc is formed. Then the water is held in sedimentation basins and the floc is allowed to settle to the bottom of basins by gravity where they are removed.

The next step in the water treatment process is the infusing of the water with ozone gas and the first of two disinfection steps. This step is not used in every water treatment plant. Ozone is highly effective in eliminating the Cryptosporidium bacteria and other naturally occurring microorganisms present in water. Unlike ultraviolet and chlorine disinfection systems (which are still used in many locations), there is no re-growth of microbes after ozonation. Ozonation also reduces the formation of trihalomethanes (chlorine breakdown products) because of the reduction of organic materials in the water before chlorination.

The final steps in the water treatment process is the second disinfection, fluoridation and the addition of a ammonium hydroxide to adjust the pH slightly to prevent corrosion of piping and fixtures of the plumbing systems in customer homes to prevent the leaching of lead into water. Nine months of the year Fairfax Water chloramine as the final disinfection step. However, during April, May and June of every year Fairfax Water flushes the entire 3,200 miles of water main and uses chlorine during that time to disinfect the delivery network. During the spring flushing program, free chlorine is added during the treatment process instead of chloramines. Free chlorine is better suited to remove residue that may have collected in the pipes.

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