YMCA of the USA and the National Lightning and Safety Institute recommend that both outdoor and indoor pools be cleared during a lightning and thunderstorm. We follow the 30-minute rule at all of YMCA of Greater San Antonio pools.
That means all Y pools (indoor and outdoor) close for 30 minutes after the last clap of thunder, or sight of lightning within a 12 mile radius of the pool. Members and guests must move off the pool deck to wait out a delay.
Why do we close our indoor pools during a storm?
Water is an excellent conductor of electricity. Just because a pool is surrounded by a structure does not make it safe during a storm.
That's why we follow the National Weather Service motto: When Thunder Roars, Go Indoors.