Swimming pool leak detection basics

How much water loss is normal?

There’s no standard formula. Evaporation can range from about 1/8 inch to 1/2 inch a day. It goes up with sun, wind, low humidity and water that’s warmer than the air, and it depends on the pool’s surface area, not its depth.

In North Carolina, a pool you never top up will evaporate completely within a year, so a falling water level is normal. What matters is whether it’s falling faster than it should.

A simple bucket test

This is a cheap way to tell evaporation from a leak.

• Fill a 5-⁠gallon bucket with pool water to within 1 to 3 inches of the top.
• Set it on the first step, weighted with bricks so it stays put, with the pump off.
• Mark the water level inside the bucket and the pool level outside it.
• Wait a day or two and compare. If the pool has dropped more than 1/4 inch beyond the bucket, the pool is probably leaking.

Why leaks are expensive

Every gallon you add also needs chemicals, and sometimes phosphate removal. Low water can damage pumps and plumbing. Many service contracts leave maintaining the water level to the homeowner, so a slow leak can run for a long time unnoticed.

How much water is that?

A leak of 1/2 inch a day adds up quickly. These are approximate loss figures for common rectangular pools:

• 14 × 28 ft (392 sq ft): about 122 gallons a day, or 44,530 gallons a year
• 15 × 30 ft (450 sq ft): about 140 gallons a day, or 51,100 gallons a year
• 16 × 32 ft (512 sq ft): about 160 gallons a day, or 58,400 gallons a year
• 18 × 36 ft (648 sq ft): about 202 gallons a day, or 73,730 gallons a year
• 20 × 40 ft (800 sq ft): about 250 gallons a day, or 91,250 gallons a year
• 40 × 75 ft (3,000 sq ft): about 935 gallons a day, or 341,275 gallons a year

Why pools leak

Newer pools: glue joints, and damage from heavy equipment during decking.

Older pools: roots, settling, cracked tile or grout, PVC pipe passing through the shell, and expansion and contraction.

Common backyard pool leaks

• The multiport valve gasket on the equipment pad
• Light conduits
• Hairline cracks in the skimmer throat
• Channel drains

It costs much less to pay for leak detection and repair than to keep refilling and treating the water.