Drought, evaporation, and pool water levels in Austin

In mild spring and fall weather, evaporation from an uncovered Austin pool runs roughly half an inch to an inch per week. In peak summer heat, especially during a heat dome or prolonged dry stretch, that number can reach 1.5 to 2 inches per week for a typical residential pool.

Features dramatically increase evaporation. A waterfall or raised spa with a spillover running several hours daily can double the evaporation rate compared to a still pool in the same conditions. The additional surface agitation and spray increases the water-to-air contact area and accelerates loss.

An auto-fill is a float-valve assembly, usually inside the skimmer or a dedicated fill chamber, that opens a water supply line when the level drops below a set point and closes when it rises again. Functionally it works like the float valve in a toilet tank. When working correctly, it keeps the pool level consistent without owner intervention.

The limitation is that a working auto-fill can silently compensate for a leak. A pool losing 2 inches per week from a crack or failing fitting will constantly trigger the auto-fill, and the owner may never notice the level dropping because the auto-fill immediately replaces the lost water. This is why a bucket test (see pool leak clues) is worth doing periodically, especially if the auto-fill seems to run more than expected.

Austin Water implements a tiered drought response plan. Lower stages typically restrict outdoor irrigation schedules but allow pool topping off. Higher stages may restrict or ban new pool fills and limit how much water can be added to maintain an existing pool.

The key distinction is between topping off an existing pool to replace evaporation and filling a pool from empty. Replacing evaporation loss is generally treated more permissively than a full refill. However, stage rules change, and the only reliable source is Austin Water's current drought stage page. Your service provider cannot override utility restrictions, but they can help you understand what constitutes a top-off versus a fill.

Austin tap water is moderately hard, typically in the range of 150 to 250 parts per million of calcium hardness depending on the water source and season. Every gallon added to the pool brings calcium with it. During a dry summer where the pool is replacing significant evaporation weekly, the calcium hardness can rise noticeably over a season.

This is not a reason to panic or drain. It is a reason to test calcium hardness regularly and understand where it is trending. Pools with calcium hardness consistently above 400 to 500 ppm start to risk scale on heat exchanger surfaces, tile grout, and salt cell plates. The management strategy is adjusting pH and alkalinity to keep the overall saturation index neutral, not chasing calcium down with partial drains.

The bucket test is the standard home method. Fill a bucket with pool water, set it on a pool step so it is submerged to the same temperature as the pool, mark the water level inside and outside the bucket, and wait 24 to 48 hours. If the pool loses more than the bucket, you likely have a leak in addition to evaporation.

Leak detection is more complex from there and usually requires a professional inspection to identify the source. But the bucket test tells you whether what you are seeing is normal evaporation or something that warrants further investigation.

A solar cover (bubble cover) reduces evaporation by 70 to 90 percent when it is on the pool. In Austin's summer conditions, this translates to a meaningful reduction in water use and a reduction in chemical consumption, because the evaporated water that would have been replaced (and its chemical content) stays in the pool.

The tradeoff is that solar covers trap heat and can push pool temperature above comfortable swimming range in peak summer. In July and August, many Austin pool owners use solar covers in spring and fall but remove them in peak summer when the goal is to cool the pool down, not heat it up.

Draining and refilling should be a last resort, not a routine evaporation management strategy. Full drains are warranted when total dissolved solids (TDS) reach levels that affect water quality and cannot be addressed by partial dilution, or when a plaster or surface repair requires an empty pool. They are not warranted simply because the pool has been evaporating heavily.

A partial drain, replacing 20 to 30 percent of the water, is sometimes used to dilute elevated TDS or calcium hardness without the risks of a full drain (floating, cracking, and the large water volume needed). Discuss with your service provider before draining any significant volume.