What Happens If a Swimming Pool Overflows?

Swimming pool builders often install overflow drains near the rim of the pool that prevent flooding most of the time. If you don't have an overflow drain, or if it is clogged, it is possible for periods of unusually heavy rain to overflow your pool. During the fury of a hurricane, for example, heavy rains can easily cause a pool to overflow. You can also cause problems yourself if you inadvertently leave a hose running too long when refilling it.

Aerial view of people enjoying the pool with inflatable tubes
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Usually, overflowing pool water is a fairly minor issue, and any overflowing waters that spill onto the pool deck or into the yard will evaporate on their own. There are steps you may have to take, however, if the flooding is excessive. After an extreme overflow, you will need to remove water from both the outside and inside of the pool. You may also need to adjust your pool chemicals, since the extra water may dilute the water and reduce the effective chemistry.

Water Outside the Pool

If your swimming pool overflows badly, you can expect the surrounding pool deck and landscape to flood with the excess water. If you have a concrete patio area or if your pool is in an area with good drainage, the flooding should be relatively minor and evaporate or be absorbed by surrounding soil in a few days. But if your pool area does not have adequate drainage, it might require that you manually remove the water by sweeping it off the pool deck or even pumping it out of low-lying landscape areas.

Items in the area surrounding the pool may also sustain water damage. So if you know heavy rains are coming, put away lounge chairs and other poolside decorations to keep them safe. If heavy winds are expected, some pool owners submerge poolside furniture into the water until the danger has passed.

High Water Inside the Pool

For a pool skimmer and filter pump system to work effectively, the water level must be at about the half-way point on the skimmer. This allows for the most efficient flow of water through the filter system. If the water level is overflowing the skimmer, you will have to remove some of the excess water in order to restore the filter system to proper function.

If you were emptying the pool completely, a rented sump pump would be the best approach, but when you need to remove a small amount of water, there are cheaper an easier methods.

Using a Filter Pump Spigot

If your pool's filter pump has a built-in hose spigot, removing excess water if very easy. Just attach a garden hose to the spigot, put the other end of the hose into the drain or area where you want water to drain, then open the spigot and turn on your pool's filter pump. Excess water will drain away. Watch the water level carefully, and stop removing water when the water level reaches the halfway point on the pool skimmer.

Use the Pump Drain Plug

Excess water in the pool can also be relieved by removing a PVC plug on the body of the pool pump. This can be removed by any large wrench—or you can buy a special plug wrench for this purpose.

Remove the plug, then turn on the pool pump. The water will begin to gush out of the pump drain plug. Monitor the water until the level is back down to the halfway point on the skimmer. Then, stop the pump and reinsert the drain plug into the pump.

Using a Sump Pump or Utility Pump

Large pools with lots of water may require a motorized pump to drain water out of them. Sump pumps or drain pumps can be rented at home improvement centers or tool rental outlets.

Attach a hose to the outlet on the pump (a pool hose works fine for a sump pump; a garden hose will fit onto most utility pumps.) Put the other end of the hose at your drain or wherever you want the water to drain. Lower the pump into the water, then plug it into an outlet (make sure it is a GFCI-protected outlet). The pump will come on automatically. Monitor the water level until it is back to the level you want, then unplug the pump and remove the pump from the water.

Siphoning Water

A very simple way to remove water is by siphoning. Submerge one end of a garden hose into the pool and place the other end of the hose at a lower elevation where you want the water to drain. Use your mouth (or a portable pump attachment for a drill) to suck water through the hose. When you hear the water begin to approach the end of the hose, stop sucking and allow the water to begin to drain out. As long as the exit end of the hose is lower than the level of the pool water, it will continue to drain. This method takes some time but works perfectly well.

Bailing

In a small pool, simply bailing out the water by hand is an effective way to remove excess water from a pool. It is a good method to use on above-ground pools.

Effects on Pool Chemistry

Swimming pools rely on a carefully balanced chemical cocktail in order to maintain the proper pH level, prevent bacteria and fungus from forming, maintain clear water color and generally keep swimmers clean and healthy. If the pool overflows, now only will the pool chemicals be diluted, but they may contaminate the pool deck and surrounding landscape. Removing excess water quickly is important to prevent this.

If your poor overflows, you will need to shock the pool with chlorine, then re-adjust your pH and chemical levels over the next week by continually re-checking the pool's pH with a pool test kit. If the pool was contaminated with debris or dirty water, you will have to clean or replace your filter.

Prevention

You can prevent your swimming pool from overflowing in all but the most extreme weather conditions.

  • Swimming pool drains can be installed to prevent the water from rising above a certain level in the pool. A drain will allow excess water to drain out and away from the pool.
  • Paying attention to what you are doing when you refill or add water to the pool will also help prevent overflow. Do not leave your pool alone for long periods or overnight while you are adding water to it.
  • To prevent damage to decking around your pool if it does overflow, all decking materials should slope away from the pool at a rate of 1/4 inch for every foot. This prevents potentially contaminated flooded water from running back into your pool.