Diagnose a Pool Leak: Step-by-Step Guide Before You Call a Leak Company

Step 1: Measure the Water Loss Before You Guess

Start with a number. Mark the waterline with painter’s tape, a pencil mark on the skimmer face, or a clear photo
reference. Check it again about 24 hours later from the same spot.

“It seems low” is not enough to diagnose a leak. A measured drop rate tells you whether the pool is losing a
quarter inch, half inch, inch, or more per day. That number becomes the baseline for every other test.

• Write down the inches lost in about 24 hours.
• Note whether the pump was running normally, off, or on a special schedule.
• Record rain, backwashing, heavy swimming, heater use, or overflow events.
• Turn off autofill during testing if you can do so safely.

Step 2: Run the Bucket Test to Separate Leak vs. Evaporation

The bucket test compares your pool’s water loss to a bucket of water sitting in the same environment. If the pool
and bucket drop about the same amount, evaporation is more likely. If the pool drops more than the bucket, the
pool is losing water beyond normal evaporation.

Place the bucket on a pool step, fill it with pool water, mark the waterline inside the bucket, and mark the pool
waterline outside the bucket. Recheck after about 24 hours.

Step 3: Compare Pump-On vs. Pump-Off Water Loss

Pump behavior is one of the most useful clues. A pool that loses water faster while the pump runs often points
toward pressure-side plumbing, return lines, equipment fittings, heater plumbing, cleaner lines, or water features.

A pool that keeps dropping with the pump off may point more toward the shell, skimmer throat, light niche,
waterline fittings, tile line, or another static leak point.

• Track one period with the pump running normally.
• Track another period with the pump off if safe for your pool and equipment.
• Compare drop rate instead of relying on a single glance.
• Write down whether features like spa spillovers or waterfalls were running.

Related: Pool leaks when pump is running

Step 4: Watch for a Stop Level

If the pool keeps dropping and then stops at the same height, that level is a major clue. The leak is often at
or slightly below the level where the water stops.

Do not refill immediately if it is safe to observe. Mark the stop level, take a photo, and compare that height
to the skimmer, tile line, return fittings, light niche, steps, benches, or visible cracks.

Step 5: Check the Equipment Pad

The equipment pad is the easiest place to find a fixable leak. Look while the system is running and again after
shutdown. Some leaks only show under pressure; others drip after the pump turns off.

• Pump lid, pump seal area, and drain plugs
• Filter drain plug, clamp, or multiport valve
• Heater unions and header area
• Chlorinator body, unions, and check valves
• Return-side plumbing and valve stems

A small drip can add up over hours and days. If the pad area is always damp, do not ignore it just because the
leak looks minor.

Step 6: Look for Bubbles, Air, or Losing Prime

Bubbles at the returns, a pump basket that will not stay full, gurgling, or repeated prime loss often points to
air entering the suction side of the system.

Start with visible basics: water level, skimmer weir, pump lid o-ring, drain plugs, suction valves, and unions.
Air issues do not always mean the pool is losing water, but they can overlap with suction-side leak symptoms and
make diagnosis confusing.

Related: Suction-side leak symptoms

Step 7: Check Wet Spots, Soft Ground, and Sinking Areas

Wet spots near the pool, soft soil, washed-out sand, sinking pavers, or a damp strip between the equipment pad
and pool can point toward underground water movement.

The wet spot is not always directly above the leak because water can travel under decking and through soil.
Still, the location and timing of the wet area matter. A wet spot that worsens while the pump runs is a different
clue than one that stays wet all the time.

Step 8: Use Dye Testing Only When You Have a Target

Dye testing is useful when you already suspect a specific spot: skimmer throat, return fitting, crack, light
niche, tile line, or step area. It is not a good way to randomly scan the entire pool.

Turn the pump off, let the water calm down, and place dye near the suspected area. If the dye pulls into the
spot, you may have found a leak path.

Related: Pool leak dye test