To properly design a Residential Water Well System for your home, we will need to know the number of water fixtures and water outlets. This method bases the approximate pumping capacity of fixture use, at the rate of 1 gallon per minute per fixture. This helps to avoid the possibility of undersizing. For instance, a four bedroom house with two and a half baths might have the following fixtures:

Outside Faucets:    4
Total Fixtures:      17 @ 1 GPM = 17 GPM 

The proper size submersible pump for this application would be a 1.5 HP, which would pump approximately 18-20 Gallon Per Minute. Where additional water is required for some special service, such as an in ground sprinkler system, this should be added to pumping capacity. When sizing a pressure tank for these systems, you first have to look at what the pumping capacity is. Pressure tanks are designed to hold 1/3 water and 2/3 air. The pressure tank should be large enough to allow the submersible pump to run for, at least, one minute. This allows the cold water passing by the electrical motor to actually cool it down. When submersible pumps and pressure tanks are properly sized for your water well system, they will provide years of reliable service.
Remember, a submersible pump a little too large will always do the job properly, and a submersible pump that is sized a little too small will have to be replaced or will prove unsatisfactory for your needs.