Hard water, mineral scale, and what it does to a cooler in the Truckee Meadows

September 21, 2026

Almost every swamp cooler repair in this valley is a scale story eventually. The pump seizes, the float stops sealing, the pads turn to crusted cardboard, and every one of those failures traces back to minerals that arrived dissolved in the water and never left. What makes Reno different from the desert cooler towns is that the water here is soft on average and genuinely unsteady in practice, and the Truckee Meadows Water Authority publishes the numbers that prove it. This post is those numbers, what they mean for a cooler, and the one fix that actually addresses the cause.

Where Reno’s water comes from

TMWA draws from two places: the Truckee River, treated at the Chalk Bluff plant in northwest Reno and the Glendale plant in Sparks, and more than 90 groundwater wells. River water is soft. Well water is not necessarily. TMWA states it plainly on its own sample pages: “Generally, when seasonal demands increase starting mid-April - October we will augment these increased demands with groundwater wells. The use of these additional sources can and does change the water chemistry somewhat.”

TMWA also says hardness varies by location, and publishes a separate sample page for each service area. That is unusual and useful, and it is the reason this page can give you a real table instead of a city-wide average that describes nobody.

The published table

Hardness in grains per gallon, for the four most recent published quarters, by TMWA service area:

Three things fall straight out of that table.

The valley-wide average is useless to you. Central Southeast Reno never left the 1.9 to 3.6 band across a full year. Southwest Reno covered 2.6 to 13.9 in the same year. Those two houses are twenty minutes apart and they are running different experiments on the same cooler.

Most of the valley really is soft. Five of the eight areas stayed at or under 5.5 grains in every quarter published, which is soft to moderately hard by any measure. This is not Phoenix or Albuquerque, and anyone selling you a whole-house softener on the strength of a cooler is overselling.

The two areas that spike, spike hard. Southwest Reno and West Reno both crossed 10 grains within the year. A pan drinking 13.9 grain water concentrates more than five times as fast as one drinking 2.6.

One correction worth making, because it is a claim you will see elsewhere and we ran it ourselves before checking the quarters properly: it is not simply true that the cooler season is the hard season. TMWA’s well augmentation runs mid-April through October, which is the second and third quarters. In Old Sparks the highest two readings do fall in those quarters, 5.2 and 5.4. In Southwest Reno the two highest readings, 13.9 and 9.8, fall in the first and fourth quarters instead. The honest summary is that the chemistry moves, sometimes a lot, and TMWA says so itself. It is not a clean summer-hard pattern you can plan around.

Why soft water still ruins a cooler

Here is the part that catches people out, and it is physics rather than local trivia. A swamp cooler does not consume water the way a tap does. Water is pumped over the pads, air blows through, and the water leaves the building as vapour. Every dissolved mineral it was carrying stays behind in the pan.

So the pan is a concentrator. Start with 3 grain water, evaporate half the pan and top it up, and the remaining water is at 6. Do that for a Reno summer, across 53.9 days at 90 degrees or hotter, and the pan is running at a hardness no municipal supply in Nevada delivers. Soft water does not prevent that. It only slows the climb.

What the climb does, in the order it usually bites:

• The pads go first. Mineral deposits on the intake face of an aspen pad, stiffening it into a crust. Water then channels down one edge instead of sheeting across the whole face, air passes through the dry remainder untouched, and the cooler blows warm on a 94 degree afternoon. That is the single most common repair call of the summer, and the warm air page has the five-minute check.
• The pump goes next. Scale grows on the impeller and plugs the inlet screen. A pump that is pushing against its own deposits draws more, moves less, and eventually seizes. That is the $150 to $400 line on the pricing page.
• The float is the sneaky one. A float valve seals with a small rubber seat against a brass orifice. Mineral on either one stops it sealing, and then the pan overfills and runs down your roof, which is the overflowing page. Scale on the float body itself makes it ride low, which tells the valve to keep filling a pan that is already full.
• The pan is last and worst. A crusted galvanized pan holds damp against its own seams, and rust under scale is how a repairable cooler becomes a $1,500 to $4,000 replacement.

The fix is a bleed-off, not a softener

There are two devices that address the cause rather than the symptom, and both work by refusing to let the pan concentrate.

A bleed-off line is the simple one: a small tap off the pump discharge that dumps a continuous trickle of pan water to the roof drain while the cooler runs. Because it is always removing the most mineral-heavy water in the system, the concentration never climbs far above the supply. The cost is that trickle, which is water you paid for and did not cool with.

A purge pump does the same job on a schedule, dumping and refilling the pan periodically rather than continuously. Several manufacturers sell one as a kit for their own units, and on a rigid media cooler it is usually the better buy because it flushes the media rather than just the pan.

Either one roughly doubles pad life and takes most of the load off the pump. On a cooler that has neither, it is the best money you can spend on the roof, and it gets quoted with a pad replacement or a spring start-up rather than as a separate visit.

What does not help much: a whole-house water softener. It swaps calcium and magnesium for sodium, which changes what the deposit is made of rather than how much of it arrives, and running softened water to a cooler is generally not what you want on the pads. If your house already has one, fine. Buying one for the cooler is not the move.

Outside TMWA

Three parts of the service area are not on TMWA water at all, and none of them publishes a hardness figure we could verify, so we are not going to invent one.

Sun Valley is served by the Sun Valley General Improvement District, its own water and sewer utility with roughly 100 miles of water mains and nine storage tanks. Fernley runs a municipal system whose groundwater recharge depends on seepage from the Truckee Canal. And the Carson Valley around Gardnerville has a large number of private domestic wells, which are not tested or published by anybody unless the owner pays for it.

The practical advice for all three is the same: assume you do not know, and let the cooler tell you. Pull a pad in August. If the intake face is white and stiff after one season, your water is harder than the valley average and a bleed-off is not optional. If the aspen is grey and soft, you are fine on a standard annual pad change. On a private well, we quote a bleed-off as standard rather than as an upsell, because private wells in this basin generally run harder than anything on the TMWA system.

What it costs, and what it saves

A bleed-off that doubles pad life on rigid media is deferring a $300 to $700 purchase by two or three years, and it is doing it while keeping a $150 to $400 pump alive. That is the arithmetic. The pad and service calculator will price a season for your own cooler, and if yours is already crusted and blowing warm, the repair cost calculator will price the fix before you call.