Between low humidity, high heat, and steady wind, an uncovered pool in this valley can lose a meaningful amount of water every week to evaporation alone.
Here is the part that matters: evaporation removes water, not minerals. Calcium, salts, and everything else dissolved in the water stay exactly where they are. When you top the pool back up with tap water, you add more minerals on top of what was already left behind.
Do that week after week, season after season, and the concentration only goes one direction.
What that looks like in practice
- Scale on the tile line. That chalky white or gray band is calcium carbonate coming out of solution and depositing on the surface.
- Cloudy water that will not clear. Sometimes this is fine calcium precipitate rather than dirt, which is why more filtering does not fix it.
- Rough patches on plaster. Scale can build up on surfaces as well as the waterline.
- Scale inside the equipment. This is the expensive version. Heaters are particularly unhappy about it, because deposits inside a heat exchanger both reduce efficiency and trap heat where it should not be.
Calcium hardness is the number to watch
Calcium hardness measures how much dissolved calcium your water is carrying. Commonly published guidance for plaster pools lands somewhere around 200 to 400 ppm.
Too low and the water becomes aggressive, pulling calcium out of plaster and grout to satisfy itself. Too high and it starts depositing calcium on every surface it touches. Both directions cause damage, just in opposite ways.
Unlike most pool chemistry, you cannot lower calcium hardness by adding something. The only real fix is replacing some of the water with water that has less calcium in it.
Slowing it down
- Keep pH and alkalinity in range. Scale forms much more readily when pH drifts high, so this is the cheapest control you have.
- Consider a cover. Not everyone wants one, but a cover is the most effective way to cut evaporation, and it reduces heating costs at the same time.
- Fix leaks quickly. A slow leak means constant fresh fill water, which means constant fresh minerals. It is easy to mistake a leak for ordinary evaporation.
- Watch your fill water. Municipal water in this region is not soft. Knowing roughly what you are adding makes the trend predictable.
- Plan on partial drains. Over a long enough period, swapping out a portion of the water is simply part of owning a pool in the desert. Timing matters, and draining a pool incorrectly can damage it, so this is worth getting advice on.
Do not let the tile line sit
Fresh scale is far easier to remove than scale that has been building for years. Once it hardens and layers up, removal moves from a cleaning job to a restoration job, sometimes involving bead blasting.
If you can see a band forming, that is the moment it is cheapest to deal with.
The short version
Evaporation is not optional here, but scale largely is. Keep pH in check, keep an eye on calcium hardness, and address the waterline before it sets.
We track this for the pools we service, so the trend gets caught while it is still a small conversation. Get in touch if you would like us to take a look.