I have a 4 GPM well with a little storage that supplies 3 homes. Even a 1 GPM well can supply 3 homes if you have enough storage tanks. A 10 GPM well can supply 2 homes with very little pressure tank storage. See how much the well will make in GPM on a 24 hour basis and you will know what you need. Size of pump and depth of well, and do a well and pump test. Test the well by running a wide open valve or pipe. Test the pump by running a valve or faucet that holds back about 40 PSI in the tank.