Is Rain Water Harmful to a Pool?

Living in the Sunshine State on the west coast in beautiful Sarasota is laid-back living at its best. The weather isn’t the only attractive thing about this sub-tropical paradise, it’s got plenty else to offer, from world-class beaches, to fine museums, to nightlife, and all sorts of outdoor recreational opportunities. Biking, canoeing, hiking, golf, tennis, boating, and so much more are always just around the corner.

Because of the fine weather, which does tend to heat up to toasty temperatures during the summer, rain storms are part of the equation. The rain is soothing, creating a comforting, lazy sound that falls on rooftops. It also helps to keep swimming pools quite full, but that’s not a real benefit because rain is certainly not a pool’s best friend. Though it might keep evaporation levels flat, it does far more harm than good. Most homeowners really don’t stop to think about this, but it’s the truth.

Though rainwater might be natural, just because it’s organic, falling from the sky, it nevertheless contains acidity. While most light rains won’t move the pH balance needle, a good drenching can easily do just that. Since we live in such an active area, rain storms are quite common, particularly during the summer months, when inch upon inch can fall for days.

Why Rainwater is Harmful to a Pool

In its composition, rainwater contains acids, powerful enough to throw-off pH balance and that’s not all. It also compromises the effectiveness of chlorine. When chlorine is diluted, it no longer functions as it should to keep pool water clean. What’s more, rainfall creates runoff. Though pools are often surrounded with a rim, the splashing effect can be enough to introduce fertilizers and other landscaping chemicals into a pool.

Maintaining the proper chemistry in a swimming pool can be very difficult. Heavy rain can greatly influence the chemical balance of pool water in several ways, including a serious effect on chlorine levels. While readjusting your pool water balance after a heavy rain can be frustrating and confusing, it is important to maintain your water chemistry because an unbalanced pool is unsafe to swim in. —San Francisco Chronicle

While this is typically minor, combined with pests, decomposing leaves and other debris, it becomes more problematic. The presence of rainwater alone lowers chlorine levels and that has a two-pronged effect. It not only dilutes, allowing bacteria to grow, but also create an environment which algae can begin to grow. This compromising state makes the water unhealthy to swim in and even exposes the pool’s finish and equipment to harm.

How to Keep Your Swimming Pool Well Maintained

After a steady or hard rain storm, your pool’s pH, alkalinity, and sanitizer levels, can all be affected enough to be off by considerable margins. As stated above, a light rain shower isn’t likely to move the levels off by much, but if that light rainfall happens for a few days, the chances of those levels falling off increase somewhat remarkably.

Once the rain has gone and the forecast is clear for the next several days, you should take steps to maintain your pool to return it to good health and to protect swimmers’ health as well. Here are some things you should do:

  • Clean your pool. Skim your pool and rid it of floating debris, such as bugs, leaves, pollen, and anything else that’s in it. In addition, you should manually vacuum your pool or set the automatic vacuum to run a full cycle.
  • Test the water chemical levels. Once clean of all debris, it’s time to check the pH and alkalinity levels. These might be off significantly if the rain event was hard or lasted for a long time. It isn’t uncommon for alkalinity levels to be quite different from pH levels.
  • Check the sanitizer and chlorine levels. The sanitizer and chlorine levels will also probably be off because rainwater introduces contaminants into the water. Return these to normal to again sanitize your pool.
  • Check the water level. Rainfall, of course, increases the water level in your swimming pool. Because it does, your pool might be overfilled. Simply use the “waste” setting on the filter to bring the water level back to normal.

If the rain event lasted for more than a day or was significant in amount, then you might consider shocking your pool. This isn’t absolutely necessary, but it is a good idea after a big rain storm. This is a good extra measure to take to ensure that the water is safe to swim in and help to guard against the next rain storm.

Should the water be cloudy or contain algae, shocking it is a necessity. Always avoid swimming in a pool after a rain storm, because it’s highly likely that contaminated runoff water is permeating through the water.

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