How often should you drain a hot tub in Utah?

Ask ten hot tub owners how often they drain and refill, and most will say “every three or four months, I think.” That is the standard advice, and for most tubs in most places it holds. In the Salt Lake Valley it is a little more interesting than that, and the reason is what comes out of your hose.

Why a tub needs draining at all

Nothing you add to a hot tub ever really leaves it. Every dose of sanitizer, every bit of pH adjuster, every splash of whatever was on the last person who got in, all of it dissolves and stays. Water evaporates off the top and leaves its minerals behind. So the total amount of dissolved stuff climbs from the day you fill until the day you drain.

At some point that total gets high enough that the water stops cooperating. You add pH reducer and the pH barely moves. Sanitizer disappears faster than it should. The water looks dull even when every test is in range. That is the water telling you it is full, and the only fix is fresh water.

The Utah part

How fast a tub reaches that point depends on how much dissolved mineral the fill water started with. And in this valley, that changes with the season.

Salt Lake City gets most of its water from the canyon streams. In spring and early summer, water from the Big Cottonwood plant runs about 8 grains per gallon of hardness, which is on the softer side for this area. But in summer, when demand climbs, the city supplements from deep wells, and the city’s own report puts those wells anywhere from about 10 grains per gallon up to more than 33. That is roughly a fourfold difference between the softest and hardest water the same tap can deliver in a year.

Murray is its own story. Murray City water averages about 375 parts per million of dissolved solids, but the range across the city’s wells runs up to 944. Two Murray tubs filled a month apart can start from very different places.

So a tub filled in April from canyon runoff has a long runway before it is “full.” A tub filled in August from well-heavy supply has a much shorter one. Same tub, same chemicals, same family, different drain date.

What we actually recommend

• Most tubs, most of the time: every three to four months.
• Filled in late summer: lean toward three.
• Heavy use, or a rental with guests turning over: three, and sometimes less.
• The water is fighting you (pH will not hold, sanitizer vanishes, water looks tired) before the calendar says so: the calendar is wrong. Drain it.

When we do a drain, clean, and refill, we test the fresh fill water before we balance it and note what the tap actually delivered that day. That number, not a calendar, sets the next drain date. If you do your own, a cheap test strip on fill day tells you the same thing.

When to do it, if you can choose

Spring, from canyon water, gives you the most headroom. Fall is the second-best time, because winter is when a hot tub gets used most and nobody wants to drain one in January. Avoid filling in the hottest weeks of late summer if you can help it.

If you would rather not think about any of this, that is what routine maintenance is for. We test on every visit and tell you when the water is getting close.