A swimming pool overflowing from rain is a very common problem for pool owners.
With the onset of climate change possibly increasing the frequency and severity of storms pool owners need to prepare for the real possibility of their pool overflowing from rain. And if you live in an area prone to heavy rain and storms your pool may overflow often.
When a pool overflows it not only affects the pool chemistry but can cause an algae bloom in the pool which turns the water green.
An overflowing pool floods your backyard causing damage to pool coping, patios, decks, lawns and gardens. The water may even run into your neighbor’s property causing damage to landscaping.
And what happens when you are on vacation and nobody is at home to keep an eye on the pool?
You may need an overflow system or a drain.
There are many options to lower the water level, rebalance the chemistry and prevent this problem from ever occurring again.
Table of Contents
Pool Overflowing from Rain Affects Pool Chemistry
When your pool fills with rain water it upsets the delicate balance of pool water chemistry. Pool chemicals become diluted and don’t work as effectively as they would normally. The level of free chlorine is effectively reduced causing your pool to become unsanitized.
Rainfall carries contaminants such as dirt, bacteria, pollen, algae spores and other organic material into your pool. If the level of free chlorine is too low your pool will quickly become unclean and unsafe for swimming.
Rain water is also acidic and lowers the pH of the pool water.
As soon as the bad weather has moved on, you need to lower your pool water down to its normal level. Test your pool water and adjust the chemical balance back to normality.
Read our post on How to Balance Swimming Pool Water
I recommend shocking the pool before and after a storm or heavy rainfall to kill any contaminants that have entered the pool water. It’s the only way to be sure the pool is sanitized and to prevent algae growth.
Pool Overflowing from Rain Affects Landscaping
If your pool has overflowed and is not drained to the correct level soon after it may damage the pool coping around the top of your pool.
Water gets underneath and between the pavers or tiles causing grout or mortar to wash away. Pavers can lift and crack. Timber decks can become water damaged and begin to rot.
If the ground around your pool is completely water logged it causes the earth to swell up moving pavers, pathways and decks. Excess water can damage retaining walls, fences and other landscaping features.
How to Lower Pool Water Level After Rain
How you remove water from your pool depends on the type of pool and your filtration system.
Some in-ground pools already have overflow drains built into the pool structure. The best type of pool is the infinity pool where the water is always overflowing on one side of the pool into a drain. These lucky pool owners don’t have to worry about anything!
However, I have seen many in-ground pools that do not have an overflow drain.
Most above ground pools do not have any pool overflow system. When the pool is full the water simply flows over the side.
Siphon the Water
Siphoning water from the pool is the simplest method to drain water.
When you have no other way to drain the water siphoning the pool into a drain with a garden hose may be your only solution.
You need a garden hose that will reach from the pool to a drain, stream, street, or somewhere you can drain the excess pool water.
Fill a garden hose with water.
Attach your garden hose to an outlet water tap and place the other end of the hose in the pool.
Turn on the tap until water has filled the hose and is flowing into your pool.
Turn off the water.
Close the hose by clamping or kinking the hose near the end and remove from the tap. Keep the water in the hose by stopping air entering the hose.
Take the end of the hose and place in the drain at a lower level than the pool water.
Open the hose by removing the kink or clamp. The water should flow from the pool to the drain.
Submersible Pump
If you have a pool with no filter plumbing for draining water, I recommend you purchase a submersible pool pump to drain the pool water.
You can rent a submersible pump but I recommend you buy one as they are inexpensive and you will use it many times. Renting a pump every time you want to drain water will be much more expensive than just buying the pump.
The cost of a submersible pool pump starts at around $50.
These powerful pumps will quickly drain off excess water from your pool into a drain.
Now, when there’s a storm you don’t have to worry about your pool overflowing from rain. Lower the pump into the pool, place the hose in the drain and turn it on.
These pumps are great for other applications such as draining spa pools, hot tubs, water features, ponds or any small body of water.
Use Your Filter Pump to Drain Water from Your Pool
If your filter plumbing has a valve for redirecting the water flow to a drain you can use this feature to lower the water in your pool.
All sand filters have a waste or drain position on the multiport valve.
Most cartridge filter systems have a valve to redirect water to the drain before it enters the filter tank.
When the pump is turned off, move the valve to the drain position.
Switch on the pump and run it until the water level reaches the midway mark on the skimmer box flap.
When the pump is operating, the skimmer flap is drawn open and pool water flows into the skimmer box. The pump draws water from the bottom of the skimmer box through the pump to the filter. However, we have redirected the water to the drain and not through the filter back into the pool.
Don’t forget to move the valve back to the filter position, after you switch off the pump. Never move the valve with the pump operating as it will damage the valve seals and cause leaks.
This method of draining the pool will only be able to lower the water level to the bottom of the skimmer flap. Then the skimmer box will run dry and possibly burn out your pool pump. So when using this method keep an eye on the water level to stop it dropping too much. You should only have to run the pump for a few minutes to reduce the water level back to normal.
Pump Drain Tap
Some pool pumps have a drainage tap where you can connect a garden hose.
To use this feature, connect a garden hose to the pump tap or spigot and run the other end to wherever you want to drain the water.
Open the pump spigot (or tap) and run the pump to drain the pool.
This is similar to the above method and can only drain the pool to the bottom of the skimmer box.
Read our post on How to Clean Your Pool After a Storm
How to Prevent Your Pool Overflowing from Rain
Lower the Pool Water before a Storm
When you have a weather forecast of heavy rain or many days of rainfall lower the pool water slightly to allow for the extra water filling the pool.
I recommend lowering the pool water to the bottom of the skimmer box so that the water just gets into the skimmer. This is only a few inches (50mm) of water and will usually be enough to combat most rain events. Unless a monsoon or hurricane hits draining a few inches of water is enough to safeguard your pool from rainfall.
Turn the pump valve to waste (or drain) and run the pump motor for a few minutes to lower the water level in your pool.
Note: Some pool owners turn off the pump during a storm to prevent possible lightning damage to the motor.
After the storm adjust the water to the correct level midway on the skimmer box flap. It’s much easier refilling a pool with the hose than trying to empty and overflowing pool.
It’s not a good idea to wait for the storm to hit and then drain the pool water. The drains will be full of water from your roof and other surface drains. Adding more water to the drains will only overburden your drains and possibly cause your gutters to overflow.
Install a Pool Cover
A pool cover is the perfect solution to preventing your pool overflowing from rain.
Excessive rain water dilutes pool chemicals and leaves the water unsanitized.
Rain washes contaminants and organic matter into your pool causing an algae bloom.
Pool covers are relatively inexpensive and save so much drama with pools.
Install an Overflow System
I recommend the installation of an overflow outlet pipe in the skimmer box to the drain. This will prevent the pool filling up beyond a maximum level so it can never overflow.
An overflow pipe can be installed by a competent home handyman or contact your local plumber for assistance.
The overflow outlet would be installed just above the midway water level of the skimmer box flap. Skimmer boxes work most effectively when the water level is half way up the skimmer flap. If the water is at the top of the skimmer flap floating debris will not float into the skimmer box.
This permanent solution stops any pool from overflowing during a storm or several days of rain. This is the best solution because you don’t have to do anything to prevent the pool from overflowing during periods of rainy weather.
Pool owners can go out or on vacation and not have to ever worry about their pool overflowing.
Install Overflow Drainage
An overflow system, as described above, will prevent the pool filling to the top so it can never overflow.
The next best method is to install some drainage around the pool to capture water when the pool overflows. This may be easier to install than making changes to your skimmer box.
Overflow drains won’t prevent the pool from overflowing but will drain away the excess water preventing damage to your landscaping.
Shock the Pool before Overflowing from Rain
During a storm your pool is going to be subjected to rain and wind that deposit dirt, debris, algae spores, bacteria and contaminants in the pool.
Add pool algaecide to the water to kill algae spores that blow into the pool.
Add extra chlorine to the pool before the storm to counteract the effect of the extra contaminants entering the pool water. It doesn’t matter whether you use granular pool shock, granular chlorine or liquid chlorine as long as you add more of it to the pool before the storm hits.
After the storm you will need to test the water chemistry and re-balance the water components as necessary.
Read our post on How to Prepare Your Pool for a Storm
Conclusion
Storms and heavy rainfall are a part of life and may becoming more frequent with climate change. Heavy rain will cause your pool to overflow if not managed correctly. And it’s always better to prevent something adverse from occurring rather than try to fix the damage.
The best option is to build an overflow system or drain into your pool structure so you don’t have to do anything when it rains. Otherwise, learn how to operate your pool pump and plumbing to pump water from the pool into a drain. If your filtration system doesn’t have a connection to a drain, purchase a submersible pool pump to be ready for the next storm.
Always lower the water level to the bottom of the skimmer when a storm is approaching. Throw in a bag of pool shock and that nasty storm will be no problem at all. The effort to lower the water and add pool shock is nothing compared to the nightmare of trying to clean and restore a green, algae infested pool.
