Your most burning questions about nitrates in Iowa answered
If you’ve been reading the news lately, you’ve probably seen nitrates mentioned alongside some pretty alarming headlines. We get asked about this every day. So here, straight from our water specialists who test homes across the Des Moines area, are honest answers to the questions we hear most.
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What’s actually in our water?
We typically see readings between 8 and 10 parts per million (ppm) in city water across our service area. The EPA’s legal limit (called the Maximum Contaminant Level, or MCL) is set at 10 ppm and it’s what Des Moines Water Works, Fleur Drive and McMullen Water Treatment Plants are required to keep levels below. Many homes here are thus sitting just below what regulators define as the legal threshold. Whether that threshold reflects what’s truly “safe” in the long term is a different question.
The EWG, an independent research organisation, sets its own health guideline for nitrates at 0.14 ppm, significantly stricter than the EPA’s legal limit of 10 ppm. Des Moines Water Works serves most of our area (covering zip codes like 50306, 50340, and 50023), and their water consistently tests above the EWG’s health guideline, even when it’s within the EPA’s legal limit.
Yes. Des Moines Water Works draws from several treatment plants, and the Fleur and McMullen plants tend to show higher nitrate readings. However, water from different sources gets mixed before it reaches your tap, so there’s no guarantee that living near a “lower-level” plant means your water is consistently lower. You may not be told when your supply source changes day to day.
They do. The only time nitrates typically decrease is in winter, when water isn’t moving through the ground. Once snow melts or rain begins, nitrates start entering the water supply. The more precipitation — and the less vegetation there is to absorb it — the higher the levels tend to be. Construction in your area can also affect readings. In short: levels fluctuate, often without warning.
Des Moines nitrate snapshot
Source: Des Moines Water Works annual water quality report / Environmental Working Group (EWG) drinking water database.
Common misconceptions
“Des Moines has the world’s largest nitrate removal facility, so the water is clean.”
This one comes up a lot. That facility is real, and it does remove nitrates, but not from all the water, all the time. What it does is treat a batch of water to near-zero nitrate levels, then mix that treated water with untreated water to bring the combined result below the legal limit of 10 ppm. “Removal facility” doesn’t mean “all nitrates removed.”
“I need to treat my whole house to protect myself from nitrates.”
Not necessarily. Nitrates are only a concern when ingested; they cannot be absorbed through the skin. Showering, washing dishes, and doing laundry in water with elevated nitrates is not a health risk. A point-of-use drinking water system (like a reverse osmosis unit under the kitchen sink) addresses the water you actually drink and cook with.
“My home test kit showed dangerous levels.”
Be cautious with consumer test kits, especially ones marketed for fish tanks or aquariums. These often measure in different units or use different chemistry, and can give readings that don’t match professional tests. If you’re concerned, ask a water specialist to test your water with calibrated equipment and give you an exact ppm reading.
“Farmers are to blame.”
Agricultural runoff is a contributing factor, but it’s not the whole story. Farming practices, chemical use, inadequate protection for rivers and streams, and yes, residential lawn fertilizers (RoundUp) all play a role. Anything washed into a storm drain goes directly to the water treatment plant. It’s a shared, multi-layered problem.
What a legitimate water test looks like
What should a proper in-home water test include?
Before recommending any treatment system, a qualified specialist should test for at least four parameters: hardness, Total Dissolved Solids (TDS), chlorine, and nitrates. They should also ask how many people live in your home and, ideally, how many gallons of water you use per month. A legitimate test is based on your actual water, not on your address, your home’s assessed value, or assumptions about what’s common in your neighborhood. Culligan Des Moines performs these tests free of charge.
What should happen after a system is installed?
After installation, any reputable company should verify the system is working, not just assume it is. For
drinking water systems, this means a leak test, a production rate check (is the system making as much
water as it should?), and a TDS rejection test. At Culligan of Des Moines, we aim for 90% or better TDS
rejection, meaning if your incoming water reads 500 ppm, the treated water should come in under 50
ppm. Ideally, a before-and-after nitrate test should be done in front of you, so you can see the result with
your own eyes.
How to evaluate any company (including us)
What certifications should I look for?
NSF certification is the most commonly cited, but pay attention to what exactly is certified. Some companies advertise NSF ratings that apply only to the structural components of the tank (its ability to withstand pressure, for example) — not to the system’s actual ability to remove nitrates. Ask specifically: “Is this system NSF-certified for nitrate reduction, and can you show me the performance data sheet?”
What are the red flags in a sales pitch?
The biggest one: being told you need a nitrate treatment system without the salesperson first testing your water and showing you the result. If someone claims your water has 100 ppm of nitrates, be skeptical immediately: At that level, the municipal utility would be legally required to issue a public health alert and shut down supply. Ask for the specific measurement, and compare it to what Des Moines Water Works publishes. Other warning signs include long high-pressure demos, prices that drop dramatically the moment you try to leave, and salespeople who can’t (or won’t) provide warranty documentation or service after the sale.
What questions should I ask before buying anything?
What does the warranty cover, and for how long?
How do I know when the system is working (or when it isn’t)?
How often does it need servicing, and who does that?
Can you show me a certified performance data sheet for this specific system?
What happens if I move? Does the system still work on a different water supply?
Understanding your treatment options
What percentage of nitrates do Culligan systems remove?
It depends on the system. Our under-sink reverse osmosis (RO) units are certified to remove nitrates — the current model achieves around 73-97%. Our whole-house nitrate-specific system removes approximately 99%.
Should I get the whole-house system for maximum removal?
For most people concerned about nitrates specifically, the answer is no, and here’s why: You only drink about 1% of the water that passes through your home. Treating 100% of it to remove nitrates from the 1% you drink is more expensive to run and doesn’t address the many other things a reverse osmosis (RO) unit removes (TDS, chlorine, and other contaminants). The reverse osmosis system is cheaper, more practical, and does more for your drinking water quality overall.
If you have reasons to believe 100% nitrate removal is best for your individual circumstance, a whole-house system with a nitrate-only option exists. It won’t soften your water or filter other contaminants. Most specialists would recommend starting with a whole house water softener that takes care of hard water (and related issues like skin and hair problems) and adding a point-of-use RO for drinking water.
Do you have additional questions?
Just give us a call on (515) 762-5304 or fill out the form below. We have three generations of
experience with the water from Altoona, Ankeny, Polk City to Clive, West Des Moines and Waukee.
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