The pool will only overflow by the amount of rain in excess of the amount of rain needed to fill the pool to the top. So if your pool is the normal 3” below the top, the rain would need to exceed 3” before any additional rain would be available to overflow onto the deck.
Typically, pools lose water for one of two reasons: Evaporation or a leak. Evaporation naturally occurs in any body of water, but it may increase under certain conditions, such as hot, humid weather. Leaks, however, indicate a bigger problem that a professional may need to address.
Pool Is Losing 1 Inch of Water Per Day
Losing more than ½” of pool water per day indicates you likely have a leak in your pool's structure or your pool pump system. You should call your pool service for a thorough leak inspection. You might not be able to keep up with refilling your pool at this point.
If pool owners or maintenance workers are constantly filling up the pool, there may be a leak. On average, swimming pools lose about a quarter of an inch of water each day, yet variations in wind intensity, humidity and sunlight can drastically change water loss rates.
You can do the “bucket test” on your pool to measure evaporation. Place a bucket of water beside the pool and mark both the water in the bucket and the pool water level. Wait 24 hours then check the loss of both. If the pool loses more water than the bucket, then you have a leak.
If your pool lost water overnight and it is more than the quarter-inch due to evaporation, you probably have a leak. Evaporation accounts for a minor amount of water lost each day. Losing a half-inch or more overnight indicates a problem.
Go to the edge of the swimming pool in the area where you think the leak might be. Without touching the water, squirt the dye in the water close to the surface and the wall. If the leak is near, you will see the dye move towards the exaction location of the leak like a current.
Look closely at the filter, pump, heater, and pipe valves, which is where leaks often tend to occur. If you have a vinyl pool liner, look for tears or separations around the fittings, lights, steps, and corners.
This will vary depending upon several factors including: weather, if the pool is covered or not, bather load, and if it is heated or not. With pools that are covered, a good rule of thumb is that they should not have to be refilled more often than once every 2 weeks.
If your pool pump manufacturer has declared your pump is rain safe, you can leave it on in rainfall. Nevertheless, during a thunderstorm, it is highly recommended that you switch off and unplug your pool pump to prevent any costly and irreversible damages to your pool equipment.
Give your pool a good shock treatment 1 to 2 days before the storm hits. You can bring the chlorine level up pretty high to prolong the pool being depleted of chlorine.
When preparing your pool for a storm, leave it uncovered. Installing any kind of cover across the pool will not do much to protect against dust and contaminants because storms often bring strong winds and heavy rain that can cause the cover to lift off your pool.
Effect on Pool Water pH
Since rain is diluting your pool, you may expect that it will reduce the acidity of your pool water. However, all rain in the US is acidic due to pollution, so rain actually decreases your pool's pH – in other words, the pool water becomes more acidic.
Shock the pool
It's not time to fix your pool chemistry just yet – that said, there's nothing wrong with giving your water a little boost. After heavy rainfall, your pool's chlorine levels will be much lower from fighting off contaminants. Shocking your pool replenishes the chlorine lost from the rain.
Protect the pump motor from water damage
In addition to removing circuit breakers, consider moving the motor indoors or covering it with a waterproof material to prevent water from getting inside.
The rule of thumb is generally 8 hours, although it could be anywhere from 6-12 hours, depending on your pool's size. Each pool is unique, so to keep your pool pump efficient and effective, you need to figure out exactly what your pool's turnover rate is.
Pool industry experts recommend you drain your pool and refill it every five to seven years. No two pools are alike, so there is no set number at which you must drain your pool.
But did you know there's an easy way to reuse the water that's already in the pool? All you have to do is recycle it! Meet reverse osmosis — the best way to purify your swimming pool water. It works by pushing the existing water through semipermeable membranes that hold off any impurities, particles, and buildup.
So, as we all know, swimming pools, whether common or privately owned, need to be cleaned on a regular basis to prevent bacterial contamination, algal growth, dirt, excess chemicals, and other things.
It's best to run your pool pump during the day
Not only does sunlight give fuel for algae to grow, it also destroys your pool chlorine and this is why you should always run your pool during the day!
In theory, if you have a cloudy swimming pool, you can add chlorine to “shock it” and clear things up. Chlorine will get the job done. But, the amounts may vary and you may have to really pound the pool with chlorine to get the water totally clear.
I think the answer to your question is about 3-6 days. The problem is that the chlorine that you need to keep the bacteria in check is used up more quickly as the temperature rises, the activity increases, and as sweat and other body stuff is put into the pool.