Every facility should have a written policy for lightening so we follow what is published by the facilities we use.   The policies are usually directed by the codes of the Department of Public Health Swimming pool division for the state the pool is in.   We do not have a separate policy since it would be superseded by these regulations.

 Here is some background information as we have been answering this question for many years now.  We think USA Swimming always needs to stress this is strictly the call of the FACILITY according to their policy and procedures manual.  We should not recommend clearing or not clearing the indoor pool.

If the pool meets state safety codes the chances of lightning striking someone in an indoor pool - through say a window - are no greater or worse than lightning striking someone through a window sitting at a desk in an office.  Local electric codes on commercial use pools usually require the pools to be grounded with a copper wire of sufficient gauge (depends on pool size) to be run around the perimeter and in full contact with the pool.  Most buildings if struck would ground the electrical current of the lightning way before it even got to the pool, hence all the other electrical and metal parts that make up a building.  You are just as safe during a thunderstorm in an indoor pool as you are in any building properly designed.

ARTICLE - Aquatics International - Risk Management: When Lightning Strikes ... While there are many urban legends in the world of aquatics, one is by far the greatest of all — lightning and indoor swimming pools.  Since many of their articles are archived you will have to go to their web site and do a search for articles.  

For every article or published information saying indoor pools are safe from lightening,  we can show that much information claiming indoor pools should always be cleared during a storm.  It is strictly the call of the facility.  – Lightning around indoor pools has been a subject debated for decades.  The proponents for one side or the other are as polarized as Democrats and Republicans.   

Here's the link with the National Lightning Safety Institute with guidance on pools   

They recommend using a "weather radio" or the TV weather channel and a cautionary approach when it comes to indoor pools.  They also recommend suspending activities when lightning is within 6-8 miles.  Dry areas inside large permanent buildings are safer than those near electrical conductors, equipment, metal objects (lifeguard stands, ladders, diving boards and water including showers).

The leading national water safety organizations including; the National Lightning Safety Institute, the American Red Cross, and the National Swimming Pool Foundation, recommend evacuating indoor pools in the event of lightning storms. Observable lightning effects inside pool buildings have included:
main circulation pump destroyed, injuries to employees touching electrical panels; concrete footing on slide blown apart; and visible lightning inside the natatorium.   then type in lightning into search box. 

In the final analysis, it is solely up to the aquatics director and pool management as to their policy.  They will always take the conservative approach as advised by Risk Management.   If the “freak accident” does occur and someone is injured in an indoor pool by lightning, the pool has no chance of defending themselves in a lawsuit.