--- title: "When to Drain a Las Vegas Pool: Not in Summer" description: "Most Las Vegas pools cannot be safely drained from May through October. Here is what happens to a pool shell in desert heat, and what to do instead." publishedAt: 2026-06-09 author: "michael" tags: ["pool care", "las vegas", "water chemistry"] --- Last week I got a call about a green pool. The homeowner had been dealing with algae for a few weeks, had tried shocking it twice, and had come to the same conclusion a lot of people reach when a pool looks bad enough: just drain it and start fresh. It was the first week of June. The high that week was 100. Draining was not an option. The instinct to drain makes sense. When water looks like that, the natural response is to get rid of it. But in the Las Vegas Valley, draining a pool at the wrong time of year turns a chemistry problem into a structural one. And from May through October, almost every day is the wrong time. ## The 85°F Rule Pool service professionals generally use 85°F as the threshold: if air temperatures will exceed 85°F during the drain or while the pool sits empty, you do not drain. In Las Vegas, highs stay above 85°F from May through October. Six months when a drain is actively risky. The rule is not conservative caution; it is based on what happens to a pool shell when the water is gone. Air temperature is only part of the picture. Ground and deck surfaces in Las Vegas summer absorb and hold far more heat than the air reading suggests. An empty pool shell sitting in that environment is not just exposed to triple-digit air. It is surrounded by surfaces that are significantly hotter. ## What Happens to a Pool Shell Without Water Water does more than fill a pool. It regulates temperature. It acts as a buffer against thermal shock. It exerts pressure outward against the walls and floor, counteracting the pressure of the surrounding soil pushing inward. When you remove that water in summer heat, several things happen. **Plaster damage** is the most common and most expensive outcome. Pool plaster that has been submerged for years holds moisture throughout its surface. When you drain quickly and expose that plaster to direct desert sun, it dries out fast. The surface layer contracts from the heat. Micro-cracks form. In severe cases, sections of plaster blister or pop off entirely. A drain-and-refill that was supposed to fix a chemistry problem can easily turn into a replaster job that costs several thousand dollars. **Fiberglass pools** are vulnerable to a different kind of damage. Without water inside, the shell can flex under the weight of the surrounding soil and its own structural stress points. Fittings and returns that are designed to sit in a full, pressurized shell can crack or pull away. Fiberglass can also warp from uneven heat exposure if the pool sits empty in desert heat. ## The Las Vegas Draining Window In practice, the safe draining window in the Las Vegas Valley runs from late October through late March. That is when sustained high temperatures stay reliably below 85°F and the risk of heat damage to the shell drops to acceptable levels. Before any drain, I check the 10-day forecast. The pool needs to be drained, serviced or repaired, and refilled within the window. A drain started in late March that runs into an early heat spike in early April is still a problem. The forecast matters as much as the calendar. Within the safe window, draining is sometimes the right answer. Outside of it, in almost every case, it is not. ## When Draining Actually Is the Right Call There are legitimate reasons to drain a Las Vegas pool. Understanding them helps clarify why algae is almost never one of them. **Cyanuric acid lock** is the most common reason I schedule a drain. Cyanuric acid (stabilizer) does not dissipate from pool water on its own. Over years of adding stabilized chlorine, CYA can build up to levels where chlorine becomes effectively unusable. Once CYA builds up well beyond the effective range, chlorine loses its sanitizing ability regardless of how much you add. The only fix is to dilute the water, which in severe cases means a partial or full drain during the safe window. **High total dissolved solids** is a related issue. Every chemical you add to pool water leaves a residue. Calcium, salt, minerals, and chemical residue accumulate over years. At a certain point, the water becomes chemically saturated in ways that affect how chemicals perform and how the water feels. A fresh start with new water, done at the right time of year, solves a problem that chemistry management cannot. **Replaster and structural work** requires draining by definition. Scheduling this in fall or early winter gives contractors the right conditions and gives the new surface time to cure before it goes back into summer service. ## What Algae Actually Needs The pool I looked at last week did not need a drain. It needed chemistry. A green pool looks like a water problem, but it is a chemistry and filtration problem. The algae in that water is there because one or more conditions were out of range: phosphate levels feeding the bloom, inadequate stabilizer letting chlorine burn off too fast, a filter that had been reseeding the problem with every pump cycle. Draining would have removed the visible algae. It would not have changed the tap water phosphate levels coming back in, or the stabilizer that was not being maintained, or the filter that had not been cleaned properly. The pool would have gone green again within weeks of being refilled. For a full breakdown of how Las Vegas algae blooms actually develop and what recovery requires, see [Why Pool Algae Keeps Coming Back in Las Vegas](/blog/algae-recovery-las-vegas/). Beyond the chemistry question, draining wastes thousands of gallons in a region where water supply is a real and documented constraint. The Southern Nevada Water Authority manages one of the most water-stressed allocations in the country. Draining when a chemical treatment would have solved the problem is not just a structural risk. It is unnecessary waste. The pool I looked at last week was cleared without draining. The water is clean now. It took the right sequence of chemistry work and filter cleaning, not a fresh start. That is almost always how it goes.