You should not drain a pool unless you have a very specific reason to do so, and/or you are doing it with the assistance of a pool professional. A fiberglass pool with no water in it is like a giant bathtub, and if the water pressure in the ground is more than the force keeping the pool in the ground, you can have what is known as a “pop out”. This is very expensive problem to have to address.
Gunite Pool
The same goes for a gunite pool. The gunite pools are usually equipped with a hydrostatic valve who’s job is to pop open if the ground water pressure is more than the water in the pool. Again, providing this is working properly, you should be fine. In the case of performing an acid wash on a gunite pool, or when we are doing a re-marcite or re-pebble job, our crews will also drill holes in the bottom of the gunite pool to allow any ground water to come through the holes while work is being performed.
Vinyl Liner Pool
A vinyl liner pool is the least expensive to fix if you “accidentally drain the pool” or if you have problems. The liner depends on water to keep it set properly in the bottom of the pool. If you drain a liner pool, the liner can shift and cause wrinkles or bubbles to get trapped under the liner. Is this a major problem? Not really, the pool should still be able to function and hold water. It may not be pretty or aesthetically pleasing. If you have continual water problems under the liner, you may need to address the drainage or add a sump pump system to help handle the ground water. In the worst case, if you need to redo a liner you are talking thousands of dollars versus the case of a fiberglass or gunite problem which would more likely be tens of thousands.
Empty Fiberglass
What can go wrong: