A picture of a pool and pool deck during a rain storm with the words "Rain

A pool is more than just water, so it makes sense that rain would affect it in some way or other. If it’s just rained and you’re considering going for a swim, you may wonder if it’s a good idea.

The truth is that unless it’s been a very light rain, you shouldn’t go swimming immediately after it’s rained; the effect rain has on pool water makes it unsuitable to swim in directly after a storm. Here is what rain does to pool water:

Affects Chemical Balance

As you may expect, rain dilutes your pool, which upsets the balance of chemicals in your pool. But rain also has other effects which change the chemical balance in your pool, so it’s best to check your pool chemical levels carefully after every rain.

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.

The pH of pool water should be kept between 7.2-7.8 because this is what the pH of a person’s body is usually at. If pool water becomes too acidic, it can irritate your skin.

An increase in pH will also reduce the effectiveness of your pool’s chlorine. To make sure that your pool can fight germs effectively, you should check and rebalance both the pH and chlorine levels of your pool after it rains.

Effect on Total Alkalinity

The diluting effect of rain will reduce the total alkalinity (TA) of your pool water. A balanced TA helps ensure that your pool’s pH remains stable. In addition, a TA that’s too low can corrode your pool and promote algae growth.

Effect on Calcium Hardness and TDS

Neither the dilution of the pool nor the acidity of the rain will really affect the calcium hardness or total dissolved solids (TDS) in your pool. However, rain will wash minerals and dirt off your pool deck and into the water, which may increase the calcium and TDS in your pool. This runoff can also affect your pool’s pH and TA.

To make sure that your pool remains safe to swim in, you need to rebalance your pool chemical levels before taking a dip after a rain.

Pollutes your Pool

Heavy rain and flooding cause run-off from your deck to pollute your pool; it can also cause run-off from surrounding plants and grass to pollute your pool. Fertilizers are full of phosphates, nitrates, and other nutrients that promote plant growth. While this is good for your flowers, trees, vegetables, and grass, it’s bad for your pool. This is because the fertilizer continues promoting plant growth in your pool – and the kinds of plant that grows in pools is algae. In other words, a pool that’s polluted with fertilizer will likely become polluted with algae soon afterwards. 

Causes Pool to Flood

As you may imagine, a pool that gets too full will flood. Your pool has drains to help combat this, but a rain that’s too heavy will negate these drains’ usefulness. To help prevent your pool from flooding, you should set your DE or sand filter to backwash before a heavy storm. If you have a cartridge filter, use the drain port to flow the water back through the system.

Erodes your Pool

A low TA is not the only factor that may erode parts of your pool. Since rain is acidic, if it’s allowed to build up too much in your pool, it may begin to erode the plaster and metal in your pool.

If you need your pool chemicals rebalanced after a storm, contact Liquidus Pool Services. They can take care of cleaning and balancing your pool chemicals on a one-time or regular basis.