Johnston does not make any of its own water. It buys every gallon and delivers it through its own pipe. That distinction shows up in the testing, and it is the whole story on this page.
There is no Johnston treatment plant and there are no Johnston wells.
Johnston's own Water Services page puts it in one sentence: "The City of Johnston purchases drinking (tap) water from the Des Moines Water Works (DMWW)." What the city's Public Works Department actually owns and maintains is the delivery network: 152.5 miles of water main, 1,974 hydrants, 1,675 valves and three storage tanks holding a combined 4 million gallons. Iowa DNR lists Johnston Municipal Water Supply, PWSID 7740011, as "Purchased Surface Water" serving 24,064 people, and its well record reads "No Well Information Found." Johnston is also one of the twelve founding members of Central Iowa Water Works, the regional production authority established April 11, 2024, with Des Moines Water Works operating the treatment plants under contract.
The 2026 joint water quality report says it directly: "The Raccoon and Des Moines Rivers are the natural resources used to make clean drinking water for 600,000 central Iowans." Three plants do that work: Fleur Drive, L.D. McMullen and Saylorville. Iowa DNR rates the Raccoon River, the Des Moines River and the alluvial aquifer beside them as "High" susceptibility to surface contamination.
Nobody publishes a plant-to-city map. The report names McMullen's customers as southern Des Moines, Waukee, Warren Water District, Clive, Urbandale and West Des Moines. Johnston is not on that list, and Fleur Drive is described as serving "all other DMWW-area customers," which points to Fleur Drive for Johnston. That is us reading the report's own wording, not a confirmed fact, and we would rather say so than pretend to certainty we do not have.
Every number below comes from the 2026 Drinking Water Quality Report covering the 2025 data year, published jointly by Central Iowa Water Works and Des Moines Water Works.
µg/L haloacetic acid annual average in Johnston's distribution system, the highest of any Central Iowa Water Works member city. The limit is 60.
2026 Water Quality Report ↗µg/L trihalomethane average, the lowest of any CIWW member city in the same report, against a limit of 80. Johnston's two byproduct numbers point opposite directions.
2026 Water Quality Report ↗wells on file for Johnston at the Iowa DNR. No local groundwater to blend in, and no municipal fallback when the rivers run high.
Iowa DNR source water ↗| Johnston distribution system, 2025 | Result | Range | Limit |
|---|---|---|---|
| Haloacetic acids (HAA5) | 24 µg/L | 15 to 45 | 60 µg/L |
| Total trihalomethanes (TTHM) | 36 µg/L | 17 to 55 | 80 µg/L |
| Chlorine (annual average) | 0.80 mg/L | 0.20 to 1.30 | 4 mg/L |
| Lead, 90th percentile | Non-detect | ND to 1 µg/L | 15 µg/L action level |
| Total coliform bacteria | 0 positive | 25 samples taken | No more than 1 per month |
Johnston's water met every federal standard in 2025. Not narrowly, either. Nothing in that table is close to a violation, and we are not going to dress it up as one.
Two of those rows are genuinely good news. Lead came back non-detect at the 90th percentile, with the highest single home sample at just 1 µg/L. For comparison, in the same report Urbandale had a sampled home at 44 and Des Moines had one at 21. Whatever else is true of Johnston's plumbing stock, lead is not the story here. Coliform was clean too: 25 samples, zero positives.
What is unusual about Johnston is the split between its two disinfection byproduct numbers. Both families of compound form the same way, when free chlorine reacts with organic matter carried in from the rivers. Johnston came in lowest in the region on one of them and highest on the other.
| CIWW member city, 2025 | HAA5 average | TTHM average |
|---|---|---|
| Johnston | 24 µg/L | 36 µg/L |
| Ankeny | 7 µg/L | 49 µg/L |
| Waukee | 8 µg/L | 61 µg/L |
| Urbandale | 9 µg/L | 70 µg/L |
| Clive | 10 µg/L | 60 µg/L |
| Des Moines | 11 µg/L | 56 µg/L |
| Norwalk | 12 µg/L | 76 µg/L |
Every neighboring member city landed between 7 and 12 µg/L on haloacetic acids. Johnston landed at 24, roughly double the next highest, with one individual sample at 45. Across the entire regional report only Bondurant, at 25, was higher. Meanwhile Johnston's trihalomethane average of 36 was the best in the group by a wide margin.
The report does not explain why Johnston's two numbers separated like that, and we are not going to invent a reason. What we can say is where it happened. This is a distribution system measurement, taken from taps out in the city rather than at the plant. Johnston buys the same finished water as Ankeny and Clive do. Something between the plant and the kitchen faucet is different here, inside those 152.5 miles of Johnston main and 4 million gallons of Johnston storage.
This matters because haloacetic acids are regulated for long-term exposure, not for what one glass does to you. EPA set the 60 µg/L limit around decades of drinking, and researchers have associated long-term exposure to chlorination byproducts with elevated cancer risk. Iowa already carries the second-highest cancer incidence rate in the country. Johnston's water is legal and it is compliant. Whether you want the highest byproduct level in the region coming out of your drinking tap for the next twenty years is a separate question, and it is yours to answer.
Central Iowa Water Works named Johnston in both of its emergency nitrate warnings.
The first Stage III ban in the region's history stopped all residential and commercial lawn watering. Johnston was one of the twelve member systems named in it. Nitrate in the Raccoon River hit 14.39 mg/L and the Des Moines River 14.04 mg/L the day it was issued.
CIWW Stage III updates ↗It happened again on June 8, with CIWW stating that the regional system was "operating at the limits of its available treatment resources." The Water Works Park infiltration gallery reached 12.3 mg/L and stayed above 10 for roughly 90 days, a record. Restrictions eased for Johnston households in phases through July 2026.
Iowa Public Radio, Jun 2026 ↗Some CIWW cities have something of their own to lean on. Ankeny runs three deep Cambrian-Ordovician aquifer wells. Waukee has one at 2,730 feet. West Des Moines operates roughly two dozen wells through its CIWW entity. Johnston's Iowa DNR file says "No Well Information Found." There is no local groundwater under Johnston to blend into the supply, so 100% of what arrives is treated river water. The bans were never about running out of water. They were about protecting the region's ability to strip nitrate below the legal limit fast enough. At the plants in 2025, nitrate reached 9.17 mg/L at Fleur Drive, 9.04 at McMullen and 4.82 at Saylorville, against a 10 mg/L limit. Those are metro-wide plant figures rather than Johnston-specific readings, because Johnston receives finished, blended water. The tap water stayed compliant both summers. The margin is what changed.
The city projects growth from 24,064 residents to 27,135 by 2030, a 12.8% increase, and names the developments driving it: Carmel Hyperion, Chesterfield Estates, Courtyards at Windsor, Crosshaven, Eagle Ridge, Enclave at Wooded Pointe, Greenwood Hills, Highgate Estates, Johnston Commons Rowhomes, Johnston Crossing and Ridgedale Heights. New kitchens in those neighborhoods almost always mean granite or quartz, which is why we drill natural stone in house instead of sending you to a countertop shop.
Census estimates put Johnston at roughly 24,384 residents across 9,260 households, with a 70.8% homeownership rate in 2024 and a median household income of $106,551, up from $103,430 the year before. An under-sink RO system is a permanent improvement to the house, and it pencils out differently when you are the one who stays in it.
There is no published median year of construction for Johnston's housing stock, so we will not guess at one, and we will not quote you a hardness number either. Hardness is not published for Johnston anywhere, and any grains-per-gallon figure you see attached to this city was invented by somebody selling something. We test your actual kitchen tap instead.
Reverse osmosis is the one household filter that meaningfully reduces both nitrate and disinfection byproducts. Pitchers and fridge filters do not touch nitrate at all.
We install the iSpring RCC7AK 7-stage system under your kitchen sink with its own dedicated faucet. Installation takes one to two hours. Pricing is $699, $849 or $1,099 fully installed depending on configuration, with no separate plumber charge.
Prime Flow Filtration does point-of-use drinking water only. We do not sell whole-house systems, softeners or well treatment, and if your situation does not call for anything we will say so and leave.
Free in-home water test, no obligation. We test your actual kitchen tap, show you the numbers, and tell you honestly whether a system is worth it.