How Does Hydrostatic Pressure in an Inground Pool Work?

Have you heard stories about entire inground pools floating or popping out? These aren’t just tall tales. Inground pools can become unstable or unsecure under certain conditions. Hydrostatic pressure is the culprit of this phenomena.

Hydrostatic pressure is the term for the force that water exerts upon other objects when it is not in motion. For example, water within a pool exerts hydrostatic pressure on the walls and floor of the pool from the inside. Groundwater also exerts hydrostatic pressure against the walls and floor of a pool from the outside.

When a pool is full, the pressure from groundwater and the pressure from water within the pool essentially cancel each other out.

If you drain a pool, the only hydrostatic pressure exerted on the pool will be from groundwater. If the ground surrounding your pool is saturated with water (either from rain or the water table), it may have enough force to harm your pool. It can cause the shell to crack, bulge or float.

This is why draining an inground pool is not recommended. If you do have to drain your inground pool for repairs, here are a few tips to follow.

How to Prevent a Popped Pool

1. Don’t Drain After Heavy Rains.

Draining your pool soon after or before a rainstorm increases the risk that your pool will pop out because of the pressure exerted by rainwater in the soil.

2. Direct the Water Far from the Pool.

Make sure to pump the water to a storm drain, or other location, that is downhill and far removed from the pool. Directing the drained water to a location far from your pool and downhill should prevent the water from seeping into the ground underneath the pool.

3. Remove the Hydrostatic Pressure Relief Plugs.

Most pools have several hydrostatic plugs along the bottom. Once the pool is drained, remove the hydrostatic plugs. You may not need to open all of them but it is important to at least remove the plug in the center of the pool floor. In most cases, the plugs are set into the plaster. You will need a hammer and chisel to break the plaster around the plug so that it can be removed. Then, you can use straight, large pliers to twist out the plug.

4. Work Fast & Refill Within a Week.

Inground pools should not be left empty for long periods of time. Along with the risk of hydrostatic pressure, plaster and vinyl pool liners can be damaged from too much dry air and sun. If you need to drain your pool for repairs, wait until you are ready for work to begin. Make sure that you have all of the supplies and materials that you need and that your contractors or helpers are ready to begin right away.

5. Hire a Professional.

If you don’t have experience draining a swimming pool, it is smart to hire a professional. Draining a pool on your own may void your warranty and cause additional damage to your pool. Hiring a qualified professional is the best way to ensure the warranty stays intact and your pool isn’t damaged in the process.

Give Pool Works a call if you need your pool drained! We are trusted by homeowners in Lakeland FL, and throughout Polk County because of our reputation for providing exceptional pool service.