How Rainwater Affects Swimming Pool Water

Without getting overly scientific, rainwater in North America is known to be acidic. As such, it can negatively affect the chemistry of a swimming pool’s water. And it can affect everything from the pH balance of the water to the alkalinity level. Aside from rainwater falling directly from the sky (and into the pool), rainwater can have other deteriorating effects. It can wash over the decking or roof, or landscaping, run off into the pool, and create pool water problems that require a fix.

Acidic rainwater can cause swimming pool water to become corrosive, with potential damage to plaster and ceramic that comprises the pool. Needless to say, light rain will have less impact than heavy rain, and this will all depend on geographic region. But whatever the case, it’s important to keep an eye on water chemistry and to ensure that everything is properly balanced. This means testing pool water on a regular basis (especially with heavy rain) and balancing accordingly.

Rainwater almost always causes pH levels in pool water to rise, and TA levels to fall (because of dilution).  When pH levels rise, it causes chlorine in the pool to “fall asleep”, which results in less effectiveness. At the same time, when TA levels fall (because of dilution) this destabilizes the pH level – it actually allows the pH to rise more quickly. These levels require ongoing monitoring.

The problem when chlorine becomes inactive is that germ killing capacity is reduced – clearly not a good thing. As for pH levels, when those go out of balance, it affects swimming comfort, causing skin irritation and eye irritation for many. Rainwater or not, water testing is essential for proper chemical balance. Many pool companies offer FREE water testing to encourage proper upkeep.

Where rainfall is consistent because of geographic location, pool owners can accommodate this with special cartridge filters and water pump settings. The fact is, light rainfall only temporarily affects water chemistry, and quite often everything balances back to normal. But whatever the level of disturbance from rainfall, there’s no need to compromise comfort or sanitation.

In cases of extreme rainfall, some pool owners resort to “shocking” the pool with special chemical compounds. Experts suggest that this isn’t a necessary action, although its still good maintenance. “Shocking” will certainly help fight contaminants, but it’s always important to follow the product instructions, to check all levels, and to “shock” in the evening hours after the rainfall has ended.

Many pool experts will remind pool owners that after rainfall, water circulation is even more critical than usual. Bacteria and algae have difficulty in moving water, so efficient circulation is key. As well, moving water optimizes the sanitizing process. Indeed, some experts suggest 10 hours of ongoing circulation after rainfall. Here, some good local advice would be helpful.

Interestingly, rainwater can also be of benefit – some pool owners actually use rainwater to top up water levels. This is clearly a water-saving approach and quite eco-friendly, but care must be taken. The rainwater must be completely filtered from all debris, and heavy downpours must be monitored in case there is overflowing. Again, advice from a pool professional would be advised.

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