Why Is My Pool Losing Water?

Every pool loses water. The question is how much. Normal evaporation runs about a quarter inch per day, roughly one and a half to two inches over a week, and more in hot, dry, windy conditions.

If you are losing significantly more than that, or if you are topping off every other day, something beyond evaporation is going on. The good news is that a simple bucket test will tell you which it is in 24 hours.

Run the bucket test first

Before calling anyone, do this. It costs nothing and it settles the question.

1. Fill a clean five gallon bucket with pool water to about three inches from the top.
2. Set the bucket on the second step of the pool so it is partly submerged and the temperatures match. Weight it with a brick if it wants to float.
3. Mark the water level inside the bucket and the pool level outside the bucket, using tape or a grease pencil.
4. Turn off any auto-fill device so it does not mask the result.
5. Wait 24 hours with no swimming. Skip the test if heavy rain is forecast.
6. Compare. If both levels dropped the same amount, you are seeing evaporation. If the pool dropped more than the bucket, you have a leak.

Run the test twice, once with the pump running normally and once with the pump off. If the loss is worse with the pump on, the leak is likely on the pressure side plumbing or at the equipment. If it is worse with the pump off, suspect the shell, the skimmer or the suction side.

Common causes that are not leaks

Splash out and carry off are real. A heavily used pool can lose an extra inch a week to cannonballs and wet towels alone.

A leaking backwash or waste valve is a very common culprit. If your multiport spider gasket is worn, water trickles continuously out the backwash line whenever the pump runs. Check for a drain line that is always damp.

Heat, wind and low humidity all increase evaporation, and so do waterfalls and spa jets, which can easily double it while they run. An uncovered heated pool loses far more than an unheated one.

Where leaks usually are

In order of how often we find them:

• Equipment pad. Pump seals, filter o-rings, valve unions and heater connections. These are the easiest to spot because you can see wet ground or dripping.
• Skimmer. The joint where the plastic skimmer throat meets the concrete shell cracks over time. A classic sign is water dropping to just below the skimmer mouth and then stopping.
• Light niche and returns. Failed conduit seals and loose return fittings.
• Underground plumbing. Harder to find, usually needs pressure testing.
• Shell cracks and failed tile grout or expansion joints.

If the water level drops and then stabilizes at a particular height, the leak is right at that level. That is a very useful clue.

When to call a professional

Call when the bucket test confirms loss beyond evaporation and a walk of the equipment pad turns up nothing obvious, or when you are losing more than about half an inch a day. Ongoing leaks are not just a water bill problem. Water escaping behind the shell erodes the soil supporting your pool and can undermine decking.

Water loss in the Florida Keys

Evaporation runs high here year round because we never get a cool dormant season, and steady trade winds pull moisture off the surface faster than still air would. A quarter inch a day is normal, but on a hot windy stretch a third of an inch is not unusual, so do not panic at a single week of heavier loss.

Salt air is hard on equipment pad hardware, and corroded fittings, unions and pump seals are a frequent source of slow loss on Keys pools. Walk your pad and look for salt crust and green corrosion at every connection.

Fresh water here comes down the pipeline from the mainland, which makes constant topping off genuinely expensive, so chasing a leak down pays for itself faster in the Keys than almost anywhere else.

Do the bucket test before you spend a dollar, because it turns a vague worry into a clear answer in one day.