If there are chemicals in the pool, that will also be diluted by the rain water. That might cause algae to break out or the pool water might look cloudy. If the rain is only light, you do not have to worry about a thing.
The Department of Environmental Health recommends avoiding activities such as swimming, surfing, and diving for 72 hours after it rains. Research has shown that the risk of infection is the highest during and the day after rain, and declines to around normal levels after three days.
Shocking your pool isn't necessary, although, it's not a bad idea either. If you get an extremely heavy rain fall, you could shock your pool for good measure. This will help fight off any contaminants that the rain may have brought to your pool.
If your pool is completely full after a storm or heavy rainfall, you don't need to take drastic steps such as emptying your pool. If you do, the hydrostatic pressure can cause your pool to come out of the ground.
It is recommended to wait at least 20 minutes to an hour after adding water balancing chemicals. You should wait 2-4 hours (or one full cycle through the filter) to swim from the moment you use calcium chloride in your pool. It is safe to swim once your chlorine levels are around 5 ppm or after 24 hours.
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.
Rain delivers algae spores and debris to pool water and it is these things that cause problems. Algae spores are usually present in the air. Riding the air currents hither and yon in order to sometimes land in hospitable locations is part of algae's reproductive strategy.
"Heavy rain dilutes pool chemicals, especially salt and chlorine, which causes the pool to turn green. This means the water is not sanitised or healthy, so it's vital to address this.
With a rain storm, any number of contaminants can be washing into your pool – acid rain, pollen, insects, tree droppings, dust, sand and even phosphates. Any one or combination of these things in rain can make your pool cloudy.
Before getting in
Don't swim or let others swim if sick with diarrhea. Shower for at least 1 minute before you get into the water to remove dirt or anything else on your body.
BUT, if you have to shock your pool during the day in broad daylight, you can still swim after adding shock. It's recommended that you wait one hour after adding shock with the filter running, and then test the water to confirm the pH and chlorine are in the proper range before letting anyone enter the pool.
Having too much chlorine in your pool water can be dangerous. Exposure to high levels of chlorine can cause lung irritation, skin and eye damage, and provoke asthma. Not only is it bad for your health, but it can be bad for your pool due to the increase in chlorine.
What chlorine level is too high to swim? It depends on who you ask, but the acceptable range is between 1 to 5 ppm. (So, for example, 10 ppm chlorine is not safe to swim in — that's too high.)
Chlorine reactions may include itchy, red skin or hives (itchy bumps). This is not an allergy but is actually “irritant dermatitis” (like a chemical burn), caused by hypersensitivity to this natural irritant. Chlorine is also drying to the skin and can irritate existing dermatitis.
Shock is liquid or granular chlorine. You should add one gallon (or one pound) of shock per 10,000 gallons of pool water every week to two weeks. During hot weather or frequent use, you may need to shock more frequently.
Best Time to Shock Your Pool
The best time of day to shock pool is when the sun is down. So, experts recommend shocking your pool in the evening or at night, to make sure it does its job. Shocking during the day can be ineffective as UV rays from direct sunlight significantly reduce free chlorine levels.
Chlorine- free shock oxidizes bacteria and organics in your pool without any additional chemicals. With this type of shock, you can swim in the pool just one hour after. Chlorine- based shock contains high levels of pH and will alter both your pH and chlorine levels in the pool.
Chlorine issues often cause cloudy water. Adding a recommended dose of pool shock to your pool can clear it right up. Poor circulation or filtration can contribute to cloudy water. Make sure your pump and filter are working properly.
You should never swim alone, always swim with a "buddy". And keep an eye on each other, even at a guarded pool or beach. And parents, keep an eye on young children even when they are with another person and a lifeguard is present. False.
The best way to determine if a body of water is safe and the risk of water borne illness is low is to sample the water and check for Escherichia coli (E. coli) bacteria. E. coli is commonly found in the intestines of humans and other mammals.
The Bottom Line about Pools and Chlorine
As mentioned above, you could probably swim in a pool without chlorine without any major health issues. However, long-term use of a pool lacking chlorinated H2O could make you sick or, at the very least, contribute to rashes and other types of skin irritation.
Rainfall dilutes pool chemistry levels and lowers the readings for pH, alkalinity, hardness, stabilizer, and chlorine. Rainfall does not contain chlorine. As well, rainfall brings with it small amounts of contaminants that are washed into the pool.
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.
At the first sign of an incoming storm, you should turn off and unplug your pump. If this is left running during a storm, the motor may suffer electrical damage and short out.