Type “Oklahoma City water hardness” into a search engine and you will get a number straight away. You will also get a different number on the next page, and a third on the page after that. We looked at the first ten results and every one of them traced back to the same water softener retailer, quoting figures between seven and eleven grains per gallon on different pages of their own site.
So we went and read the city's documents instead. Here is what is actually in them.
Oklahoma City does not publish a hardness figure at all
Hardness is not a regulated contaminant. It is a nuisance, not a health risk, so the Environmental Protection Agency does not set a limit for it and utilities are not required to report it. We read Oklahoma City's 2021 Consumer Confidence Report cover to cover and the word does not appear in the results table.
What the city does instead is ask you to telephone. Its own utilities pages direct residents with questions about hardness to the water quality line. That is not evasion — it is the honest answer to a question that does not have one number.
Because the city runs on two completely different waters
This is the part almost nobody selling water treatment in this market will tell you, and it is in the city's own Water Conservation Plan: “Oklahoma City relies on water from two sources, the North Canadian River supply and the southeastern Oklahoma supply.”
Those two supplies are not alike, and the city says so plainly.
The Hefner plant, in the northwest, takes raw water from Hefner Reservoir. The plan says that water “originates from the North Canadian River and is generally hard and high in organic matter”. It is treated with lime addition and recarbonation — which is softening, done at the plant — and it serves “the north and northwest portions of Oklahoma City”.
The Draper plant, in the southeast, treats water piped a hundred miles from the Atoka and McGee Creek reservoirs in southeastern Oklahoma. The plan says that water “is much softer and does not require treatment for hardness removal”. It serves “the southern, western, and eastern portion of Oklahoma City”.
The Overholser plant, in the middle, takes North Canadian River water like Hefner does, also uses lime, and mostly runs in summer to cover peak demand downtown.
So can you work out which one you are on?
Not reliably, and we are not going to pretend otherwise. All three plants pump into one citywide distribution system. The water arriving at a given house is a blend, and the blend moves with demand, with the season and with which plants are running. A company that tells you which plant feeds your address is guessing in front of you.
What the city already does about it
Treatment at Hefner and Overholser includes lime addition — that is lime softening, the same chemistry a water treatment plant has used for a century. It is also why the city's water quality report lists “lime and/or calcium carbonate particles from softening efforts” as a source of cloudiness in the supply.
Worth being clear about what that does and does not mean. Partial softening at a treatment plant brings hardness down. It does not produce soft water at your shower head, and it is not the same thing as an ion exchange softener in your garage. If it were, nobody in this city would have scale on their fixtures, and plenty of people do.
And the chloramine
Hefner and Overholser both finish with chloramination. Chloramine is chlorine bound to ammonia. Utilities use it because it survives longer in the distribution pipe than free chlorine does, which is a genuine public health benefit — and it is also the reason it takes more carbon contact time to take back out again. If your water tastes like a swimming pool, that is what you are tasting, and a whole-home carbon filter is what deals with it.
The only number that describes your house
It comes out of your own kitchen tap, and it takes about fifteen minutes to get. We do it free, on site, and you watch it happen rather than waiting for an emailed report.
That is not a sales line, it is the consequence of everything above. In a city that blends two source waters and publishes no figure, a test is the only honest basis for a recommendation.
Sources. City of Oklahoma City Water Conservation Plan, 2017, pages 16 to 22. City of Oklahoma City 2021 Water Quality Report. Both are published at okc.gov and both are linked from our Your Water page, so you can read them yourself.