Treatment Process

Water Treatment is a vital step to ensuring a safe high quality product is delivered to Des Moines Water Works' customers.  DMWW operates three water treatment plants in Central Iowa. Each treatment plant uses a multi-barrier approach to ensure the safety of your drinking water. This includes source water monitoring, riverbank filtration, treatment processes of softening, filtration and disinfection, as well as distribution system monitoring and maintenance. 

View a video of the water treatment process at Des Moines Water Works:

The Fleur Drive Treatment Pant has the capacity to pump 75 million gallons per day (MGD). The treatment plant at Maffitt Reservoir can pump 25 MGD.  DMWW’s third treatment plant at Saylorville pumps 10 MGD and can be expanded in the future to pump 20 MGD.

The treatment plants at Fleur Drive and L.D. McMullen treat water in a similar fashion.  A pretreatment step is completed at the Fleur Drive plant in which powdered carbon is used with the river water to reduce dissolved organic matter.  This organic matter results from the natural decay of leaves and vegetation in addition to agricultural and municipal wastewater discharges. The L.D. McMullen Water Treatment Plant does not need this pretreatment step because shallow groundwater and Maffitt Reservoir have no sediment to remove.

Lime softening is next in the treatment process for both plants. Through lime softening, hardness, germs, and bacteria are removed.   The water is then filtered through sand and gravel to remove all particles.  When nitrate levels are high at the Fleur Drive plant, a portion of water receives nitrate removal through an ion exchange process and is blended with the rest of the post-filtered water to stay safely below the EPA Safe Drinking Water Standard. The water at Maffitt treatment plant does not require nitrate removal since the shallow groundwater source contains reduced levels of nitrate compared with the rivers. The McMullen Water Treatment Plant water can be easily blended with nitrate-free water from Maffitt Reservoir to remain below the Safe Drinking Water Standard.  The final step in the process is the addition of fluoride to help prevent dental cavities and chlorine to disinfect the water.

The Saylorville Water Treatment Plant uses technology different than the two other water treatment plants.  Water is pumped from collector wells to a pre-treatment step to oxidize and remove iron and manganese.  After pre-treatment, the water is passed through ultra filtration (UF).  The ultra filtration removes any non dissolved particles larger than 0.01 micrometers (this includes virus, bacteria, and giardia).  Next, the water is sent through reverse osmosis (RO) filtration.  RO filtration will remove particles as small as 0.001 microns (this includes hardness and nitrate ions).  The final step in the process is the addition of fluoride to help prevent dental cavities, chlorine to disinfect the water, and sodium hydroxide to adjust the pH.

When the treatment process is completed at all three treatment plants, the water enters a storage tank and is eventually pumped into the Central Iowa distribution network.  All treatment plants have a sufficient number of pumps to provide a reliable supply of water at all times and emergency power supplies to maintain plant and pumping operation when electricity is interrupted.  The distribution system consists of more than 1,400 miles of pipe, 10,000 fire hydrants, 9,700 valves, 10 water storage tanks and 10 booster pumping stations.

Throughout the treatment process, DMWW’s state-certified laboratory staff performs 50 to 150 tests each day to ensure the highest quality water is produced.  An additional series of 50-60 daily tests on the untreated water sources allows the laboratory staff to identify any necessary changes needed in the treatment process before the water enters the plant. The laboratory also carries out a progressive research program and performs several research projects and studies throughout the year.  DMWW monitors and tests for emerging and unregulated contaminants to stay ahead of potential health risks, including cyanotoxins produced by cyanobacteria, Per- and Polyfluoroalkyl Substances (PFAS), neonicotinoids, and pharmaceutical and personal care products (PPCP).

Where Does Your Water Come From?
The Raccoon and Des Moines Rivers are used to provide drinking water to more than 500,000 
Central Iowans. Upstream land use practices – agricultural and urban – have a direct effect on 
water quality and quantity for downstream users. All Iowans should Think Downstream and 
consider how they can help make Iowa’s water safe for drinking and recreation. 

The Fleur Drive Treatment Plant has the flexibility to draw water from either the Raccoon River or the Des Moines River, in addition to the Infiltration Gallery (a series of underground pipes located throughout Water Works Park adjacent to the Raccoon River). The Gallery collects water from the same shallow groundwater as the L.D. McMullen plant. In an emergency situation, the Fleur plant can draw up to 6 billion gallons of water from the Saylorville Reservoir. Des Moines Water Works’ plant operators, along with laboratory staff, select the river source that has the highest quality water. 

The L.D. McMullen Water Treatment Plant at Maffitt Reservoir treats water from six radial collector wells and one horizontal well along the Raccoon River. The collection elements are located in the coarse sand and gravel formation beneath the river. The shallow groundwater receives natural filtration prior to entry into the wells. The 1.3 billion gallon Maffitt Reservoir serves as an emergency supply for the the McMullen plant.

The Saylorville Water Treatment Plant treats water from two radial collector wells along the Des Moines River.

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