Before draining a swimming pool, you must obtain a pool drain permit. The federal government amended the Clean Water Act (CWA) in 1972 to include the provision that the discharge of pollutants to bodies of waters of the United States is unlawful, unless the discharge is in compliance with a National Pollutant Discharge Elimination System (NPDES) permit. Pool water may not be drained anywhere except to the sanitary sewer system.
To drain a pool completely, you must first submit an application to obtain a pool drain permit. The cost is $183.00. You will coordinate with an inspector to work out a pumping rate and to locate a sewer clean out to drain the pool water to. The inspector will visually inspect the water and test the pH of the water. Note that if you only need to lower the height of the pool water, you can pump the water to a sanitary sewer clean out, which is often adjacent to the kitchen, for example it is to serve the kitchen sink, without obtaining a permit.
Either the pool owner or the pool contractor will need to contact the City of Gilroy Pretreatment Program, 408-846-0451 to start the process. A pool remodel that requires a permit from the Building Department would also require a pool drain permit. After approval, you will need to coordinate with an inspector to meet at the property. The inspector will determine the location to drain the pool water and then the pool can be drained and the work can be completed.