DIY Pool Repair

How To Find Swimming Pool Leaks

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• Home
  Swimming Pool Leak Detection
• Pool Resources
  List of swimming pool resources - Must read for any pool owner
• Signs of damage
  Obvious deficiencies can be a significant possibility for water loss
• Water loss characteristics
  Has the leak developed slowly over time or suddenly over a short period of time
• Pool plumbing systems
  Understanding your plumbing system is critical in being able to diagnose a leak in your swimming pool
• Hydrostatic test
  Learn how to monitor water loss and conduct a hydrostatic test for your pool
• Test Analysis
  Analyze the data from this leak detection test to find out where your pool is leaking
• Condition 1
  Leaking the same with plumbing system on and off
• Condition 2
  Leaking more when plumbing system is on, but water loss in both conditions
• Condition 3
  Leaking more when plumbing system is off, but water loss in both conditions
• Condition 4
  Leaking when plumbing system is on, not leaking when it is off
• Condition 5
  Leaking when plumbing system is off, but not leaking when it is on
• Leak detection test 2
  Another easy method to determine where your pool is leaking
• Water Level Test conclusions
  Analyze the results of the water level leak detection test
• Faceplates & Gaskets
  water level holds anywhere where gaskets or faceplates are touching the waterline
• Skimmer & Mid Wall
  water level below skimmer mouth but above return outlets
• Return Outlets
  water level holds at the height of wall returns
• Indefinite Drop
  water level continues to drain down past wall returns or lower
• Leak Detection Dye Test
  Use colored dye to locate leaks in your swimming pool
• Common Pool Leak Points
  Breakdown of pool components prone to failure and associated water loss symptoms
• Hole In the Liner
  See symptoms associated with a hole in the liner of your swimming pool
• HRV Failure
  Hydrostatic relief valve failure symptoms
• Filter Head Gasket
  Filter head gasket alignment is a common location for unexplained water loss
• Leaking Skimmer
  See symptoms associated with a leaking or cracked skimmer
• Leaking Return Lines
  See symptoms associated with leaks in the swimming pool return lines

Filter Head Gaskets

The condition where water escapes past the built in one way valve in the filter head is a major source for unexplained water loss in inground pool installations with a permanent discharge line attached to the filter. Many filter types can have this problem where a back pressure on the filter head will cause the internal gasket to shift and allow water to leak past the check valve in the filter head and drain out through the backwash line under normal pool filtering settings.



Many easy fixes are often witnessed for this condition, most commonly being a manual ball valve that prevents water from escaping into the backwash line. The downside to this easy fix is that the valve must be manually opened to backwash and manually closed afterwards.

The correct solution to this problem is to open the filter head (NOT while under pressure) and reset the gasket which will be out of its obvious position. This condition occurs when the water being pushed through the backwash line creates a vacuum after the filter is put back to “filter” from “backwash”. Changing this dial setting closes off the backwash line with a watertight seal.

The water in the backwash line is still moving however, and if there is no air gap in the backwash line (if it is full of water), a temporary back pressure is created as the water continues its path through the pipe and away from the filter. Even a small back pressure is enough to pull the gasket out of position of many models of filter.

Use this resource if you need further or more detailed information on swimming pool sand filters

Primary Leak Symptoms

A leak in the filter can be elusive to diagnose. An easy check to see if your filter is leaking through the backwash line is to remove the filter sight glass when the pool is in normal filter mode. The sight glass on the filter is designed for you to view the water clarity that is being backwashed through the filter. When in regular filter mode no water should be able to access the sight glass.


The menu on the right is a chronological step by step process to determine where a swimming pool is leaking. This website is written as a readthrough technical assistance guide for locating leaks. When you believe you have identified where the pool is leaking you need to go to our sister website to see pictures and learn more about the actual swimming pool leak repair process.