Refilling a swimming pool is necessary when water evaporates, leaks out or the pool is emptied for maintenance or cleaning. If the person refilling the swimming pool is not paying attention to the pool, or if you have a significant amount of rain fall into your already full pool, the swimming pool can overflow.
If your swimming pool overflows, you can expect the surrounding area to flood with the excess water. If you have a concrete patio area or your pool is in an area with good drainage, the flooding should be relatively minor. If your pool area does not have adequate drainage, you might be left with a large puddle of water around your pool that has to be manually drained or dried out. Items in the area surrounding the pool can also be damaged by the water.
Before you can do anything else to your pool, you will have to remove the excess water from inside of it. If your pool has a drain installed on it, you can simply remove the plug or cover from it and allow the excess water to drain out. If your pool does not have any type of drain, you will need to either have the excess water suctioned out of the pool with a pump or manually bail the water out using buckets. Remember, your pool filter and skimmer assembly should sit at the top of the water level, if it is underwater, it can not filter contaminants from the water effectively.
Swimming pools rely on a carefully balanced chemical cocktail in order to maintain the proper pH level, prevent bacteria and fungus from forming, maintain clear water color and generally keep swimmers clean and healthy while using the pool. If the pool overflows, too much water will be present for the existing chemicals and some of the chemicals may even flow right out of the pool. If your poor overflows, you will need to shock the pool with chlorine then re-adjust your pH and chemical levels over the next week by continually re-checking the pool's pH with a pool test kit. If the pool was contaminated with debris or dirty water, you will have to clean or replace your filter.
You can prevent your swimming pool from overflowing in almost all but the the most extreme weather conditions. Swimming pool drains can be installed to prevent the water from raising above a certain level in the pool. Instead, excess water is drained out and away from the pool. Paying attention to what you are doing when you refill or add water to the pool will also help prevent overflow. Do not leave your pool alone for long periods or overnight while you are adding to it if you want to avoid overfilling it.