Nitrate in central Iowa water, explained
Two mandatory watering bans in two summers. A treatment facility that ran in January for the first time since 2015. A 10 mg/L federal limit the system keeps pressing up against. Here is what is going on and what works inside a house.
What is nitrate, and why does it matter in Des Moines?
Nitrate is a nitrogen compound, and it gets into rivers mostly through agricultural runoff and field drainage. EPA sets the maximum contaminant level at 10 mg/L for public drinking water, measured as nitrogen. Central Iowa pulls its drinking water substantially out of the Raccoon and the Des Moines, and both of those rivers carry a seasonal nitrate load that gets up to and sometimes past that limit before anybody treats it.
Central Iowa Water Works brings it back under the legal limit, so what shows up at your tap is compliant. What has gotten visible is the cost of staying compliant. A dedicated nitrate removal facility running earlier and longer, and mandatory lawn watering bans across the whole system in June 2025 and then again in June 2026. For the water you actually drink and cook with, an RO system at the kitchen sink is the household method that moves the number.
The last two years, in order
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Twelve utilities become one wholesale authority
Central Iowa Water Works goes operational. Twelve founding members, and more than 600,000 Iowans on the system.
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The region's first lawn watering ban
Nitrate in the rivers forces a mandatory ban, the first one ever here. Officials said at least one source had to come in at 10 mg/L or lower before it could be lifted all the way.
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Nitrate removal runs in January, first time since 2015
The facility at the Fleur Drive plant comes online in the first week of January. By May 1 it had logged 107 days.
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Maffitt Reservoir sits 5.5 feet low
CIWW holds a press conference asking people to go easy on irrigation. Maffitt is an emergency source, and executive director Tami Madsen puts it 5.5 feet under where it ought to be.
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A Stage 2 alert asks for a 50 percent cut
Voluntary, not mandatory. Reporting the following day had the Raccoon at 17.17 mg/L and the Des Moines at 10.4.
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The second ban, twelve days later
The board enacts Stage 3 of its Water Use Plan. Summer lawn watering runs about 40 percent of the system's drinking water supply, per Madsen.
Where does the nitrate come from?
Upstream, and seasonally. A 2025 assessment commissioned by Polk County put nearly 80 percent of the nitrate in these two rivers on agriculture, broken out as roughly 40 percent surplus fertilizer, 20 percent manure and 20 percent nitrogen fixed in the soil by soybeans. So the spikes track spring rain and field drainage, and they have nothing to do with anything happening at your house. It also explains why the utility's own answer is treatment plus demand reduction. They cannot go change the source.
That is the shape of this problem. Nitrate in central Iowa is not a steady background number, it is a seasonal surge that treatment has to absorb. That is why the facility runs in stretches of weeks at a time, and why the bans land in June.
Where the 10 mg/L limit comes from
The EPA's maximum contaminant level for nitrate exists primarily to protect infants under six months of age. In that group, high nitrate intake can interfere with the blood's ability to carry oxygen, a condition clinicians call methemoglobinemia. That is the published basis for the standard, and it is why the number landed where it did instead of on something round.
For most households it reads a lot simpler than that. Compliant water is legal water. If you have an infant in the house, or somebody pregnant, or anybody a physician has told to watch their nitrate intake, you have a specific reason to treat at your own tap and not lean on the margin at the plant.
What reduces nitrate in a house, and what does not
| Method | Reduces nitrate | Notes |
|---|---|---|
| Reverse osmosis | Yes | The standard household answer. Installed under the sink for drinking and cooking water. |
| Ion exchange water softener | No | Removes calcium and magnesium. Not designed for nitrate and should not be sold as a nitrate solution. |
| Carbon filter, pitcher or whole-home | No | Good for chlorine taste and odor. Carbon does not meaningfully remove nitrate. |
| Boiling | No | Boiling evaporates the water and leaves the nitrate behind, so it concentrates. This one actively hurts. |
That table is probably the most useful thing on this page, because those first three rows are what gets sold to central Iowa homeowners who picked up the phone about nitrate. If somebody quotes you a softener and talks about nitrate in the same breath, that is two unrelated things stapled together. That is the tell.
Sources
- Central Iowa Water Works, founding entities, ciww.gov/about
- Central Iowa Water Works, Stage III daily nitrate readings, summer 2025, ciww.gov
- Central Iowa Water Works, Stage 3 water warning release, June 2026, and Iowa Public Radio coverage, June 9, 2026
- KCCI, nitrate removal facility running in January, January 11, 2026
- IIHR, University of Iowa, nitrate removal facility operating days, May 2026
- Central Iowa Source Water Research Assessment, commissioned by Polk County, released July 2025
- US EPA, National Primary Drinking Water Regulations, nitrate maximum contaminant level of 10 mg/L
Last reviewed October 30, 2026. River nitrate readings and ban status change through the season. Check ciww.gov for current conditions.
Questions we get asked
Is the nitrate in Des Moines water dangerous?
Water delivered to your tap by Central Iowa Water Works member utilities is treated to meet the EPA maximum contaminant level of 10 mg/L for nitrate, so it is legally compliant. The concern that drives the EPA standard is primarily infants under six months of age, where high nitrate intake can interfere with the blood's ability to carry oxygen. Households with an infant, anyone pregnant, or anyone advised by a physician to limit nitrate have a specific reason to treat at the tap.
Does a water softener remove nitrate?
No. A standard ion exchange softener is built to remove calcium and magnesium, the minerals that cause hardness. It does not meaningfully reduce nitrate. Reverse osmosis is the practical household method. Any quote that treats a softener as a nitrate solution is combining two unrelated problems.
Will boiling my water remove nitrate?
No, and it makes the problem worse. Boiling evaporates water while the nitrate stays behind, which concentrates it. Boiling is a response to bacterial contamination, not to nitrate.
Why does Central Iowa Water Works ban lawn watering instead of just treating more water?
Because summer lawn watering consumes roughly 40 percent of the system's drinking water supply, according to the utility's executive director. Cutting demand lets the treatment plants keep the water they do produce under the 10 mg/L federal limit. The bans are a capacity measure during high-nitrate stretches.
How do I find out my own nitrate level?
Your utility publishes an annual Consumer Confidence Report with system-wide numbers, and Central Iowa Water Works posts current river conditions. For the reading at your own kitchen tap, we test it free as part of a quote.
Find out what your tap reads
We test nitrate at your kitchen sink, free, and show you the number next to your utility's published data.