Water Supply and Treatment Division 
Everyone expects to turn on their tap
and have clean, safe drinking water
flow out. To make this happen requires
the 24/7/365 commitment of water
operations staff to ensure that an
adequate supply of drinking water - in
full compliance with all local, state and
federal regulatory requirements - is
delivered to Durham’s customers
every day. Another major public safety
aspect of the system is maintaining
adequate fire flow for fire suppression.
The staff of the Water Supply and
Treatment division operates the City’s
two water treatment facilities and the
Lake Michie and Little River Lake pumping
stations. Durham has two main sources of
raw water supply; Lake Michie
(pictured right), which was completed in
1926, and Little River Reservoir, which was completed in 1987. These two lakes have a combined safe yield of 37 million gallons per day (MGD). Lake water is delivered to the either of the City’s treatment plants using a combination of gravity flow and electric and hydro-powered pumping for efficiency purposes. The staff also utilizes time of day pumping to keep electric costs as low as possible.
The Williams Water Treatment Plant (WTP) was constructed in 1917 and has a current capacity of 22 MGD. The Brown WTP was completed in 1979 and has a current capacity of 30 MGD. The annual daily average water production of the facilities combined was approximately 28.2 MGD for 2010, with a peak daily production of 38.84 MGD on July 29, 2011.
Water Treatment Process
Treating drinking water requires water plant operations staff to carefully monitor all steps of the process to make sure that when the customer turns on the tap at home or at work, the water meets all federal and state drinking water standards. Below is a step by step description of the water treatment process.
Terminal Reservoirs and Treatment Plants
Raw (untreated) water from Durham’s two reservoirs/lakes is pumped into terminal reservoirs located at the City’s two water treatment plants. The Brown Water Treatment Plant (WTP) terminal reservoir holds approximately 90 million gallons and the Williams WTP terminal reservoir holds approximately 45 million gallons. These volumes represent a two to three day supply of water for the two treatment plants. The storage in the terminal reservoirs provide a constant supply of raw water for the treatment plants should any interruption in raw water delivery occur due to either line breaks or routine maintenance.
Coagulation, Flocculation and Sedimentation
Raw water from the terminal reservoirs 
flows into clarifiers where sediment and
other particulate matter are removed by
processes known as coagulation,
flocculation and sedimentation.
Coagulation occurs with the help of
chemicals known as coagulants that use
their positive charges to attract
negatively charged particles like sediment
and organic matter present in raw water.
Flocculation then occurs as these particles
clump together and form flocs, or clumps
of sediment and particulate matter. These
flocs then settle to the bottom of the
clarifier (sedimentation) where rake-like
structures slowly scoop the solid matter
out.
Clear, sediment-free water leaves the clarifier from the top and flows onto the next step in the treatment process. Currently, both treatment plants use a chemical called ferric sulfate as a coagulant.
Filtration
After water has gone through the flocculation and sedimentation process to remove the sediment/particulate matter, it flows through filters composed of layers of crushed anthracite coal, sand and gravel. The filtration process removes additional minute particles which are not removed by the flocculation and sedimentation process.
Disinfection and Chemical Addition
Several chemicals are added to the water throughout the different processes to facilitate water treatment. They include chemicals for disinfection (chloramines), corrosion inhibition (orthophosphate), pH balance (sodium hydroxide) and dental health (fluoride). The concentrations of each of the majority of these chemicals must meet EPA standards. Below is a brief description of each additive. For a description about Durham’s water quality in general visit our Water Quality webpage.
Chloramine (CLNH3)
The City of Durham has been using chloramination as the method of disinfection for drinking water since January 2002. Chlorine and ammonia react chemically to produce combined chlorine or chloramine, which is an effective method for killing many types of bacteria and other germs. Using chloramination helps to reduce the formation of disinfection by-products in the water distribution system. The City maintains a running annual average concentration of 2.9 mg/L or parts per million (ppm) of chloramines in water leaving the City’s treatment plants. For information on the City’s use of chloramines as a disinfectant, click here.
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Zinc Orthophosphate (ZnPO4)
The City of Durham has used zinc orthophosphate to inhibit corrosion in service lines and household plumbing since the 1970s. Phosphates create a protective coating on metal surfaces and reduce water’s chemical activity, which decreases the processes that lead to corrosion. The City currently maintains a concentration of 0.8 mg/L (ppm) of zinc orthophosphate in the water leaving the City’s treatment plants
Sodium Hydroxide (NaOH)
Balancing the acidity/alkalinity of our drinking water is a very important part of the treatment process. pH is a measure of a liquid’s acidity/alkalinity; acids have a pH below 7 and bases (alkaline substances) have a pH above 7 to 14. Stronger acids have lower pH’s and stronger bases have higher pH’s. In 2010, the pH of Durham’s water ranged from 7.3 to 7.7 (7 being neutral).
Fluoride (H2SiF6)
Fluoride in the form of hydrofluorosilicic acid has been added to Durham’s drinking water since the late 1950’s in order to prevent tooth decay. According to the American Dental Association (ADA), "fluoridation is a safe and effective means of preventing tooth decay. It has been cited by the Centers for Disease Control and Prevention as one of 10 great public health achievements of the 20th century. Studies show that fluoridation can prevent between 15–40 percent of decay." The ADA cites over 60 years of studies supporting this conclusion. The City maintains a fluoride concentration that ranges from 0.47 to 1.0 mg/L (ppm) in our drinking water.
Visit the American Dental Association for more information on Fluoride in drinking water.
Storage and Distribution
Once treated and disinfected, drinking
water is stored in covered tanks called
clear wells. The City stores several
millions of gallons of treated water in
clear wells on the treatment plant sites
ready for distribution. Treated water is
also stored in elevated and ground
level water storage tanks located
throughout the City. Levels in the
towers are monitored remotely and
generally are filled each evening using
off peak pumping strategies. Towers and
elevated tanks help maintain pressure in
the distribution system so that each household and business has sufficient flow.
Water Supply and Treatment personnel also respond to questions and complaints about water quality. In addition to daily analysis of treatment process dosages, staff also collect and analyze distribution system samples daily to monitor overall system water quality.
If you are experiencing a problem with a pink film or residue on your bathroom and kitchen fixtures, click here for more information.
For information about drinking water quality, read the most recent "Annual Water Quality Report" or call (919) 560-4362.