Most county minimum standards for a valid building site (to obtain a building permit) is one gallon-per-minute. Even though one gpm is acceptable, with a yield that low, additional storage is required. You must be able to pump five gpm for four hours once every 24 hours which is equivalent to 1,200 gallons per day. The equation used is as follows:
Minimum Water Quantity
A well intended to supply domestic water for a single family residence shall provide an adequate water supply as determined below:
Five gallons per minute for a period of 4 hours (4 hrs. X 60 min. X 5 gpm = 1,200 gallons; or,
When the well itself does not meet the criteria of (1) above, an adequate water supply may be produced from a combination of approved sources and/or storage capacity. When storage capacity is utilized, the total gallons of water available shall be equal to 1,200 gallons. That 1,200 gallons may be derived from the sum of the following:
Total well production (TWP) expressed in gallons for a 4-hour period (240 X GP = TWP in gallons);
Twenty-five percent of the total volume of the water system pressure tank (.25 X PTV = gallons);
In those wells having a static water level above the point of water discovery, that volume of water expressed in gallons, contained in the well casing between the static water level and the top of the pump (static water volume, SWV);
Auxiliary storage; auxiliary storage required may therefore be computed by use of the following formula:
1,200 – TWP - .25 PTV – SWV = Aux. Storage
Wells producing less than one gallon per minute shall not be acceptable in meeting these requirements.
The production capacity of a well shall be certified by a licensed well driller, contractor, or person licensed in the State of California for such a test or tests.
In situations where a current well exists, we highly recommend a new draw-down test be performed to determine well production, and that a potability test be done as well. You may contact our firm for free estimates of these services.
In a modern home with 2 bathrooms (3 outlets in each), a kitchen with a sink, automatic dishwasher and automatic washing machine, a laundry tub in the basement, and with two outside hose bibs, a water system with a capacity of 12 gpm would be required (or 720 gph for one hour).
For larger homes, this method provides an adequate amount of water when it is needed to match the increased demands that are required for lawn sprinkling, extra guests, and additional use of dishwashers and washing machines.
For a farm system, the home usage should be taken into account as well as the drinking requirements of the animals, the water needed for barn cleaning purposes, and an adequate capacity for fire fighting. The system should be capable of delivering this capacity continuously for a period of two hours. The time at which the water will be used must be given consideration to insure adequate pressure at all times, to avoid delays and inconvenience.
For the size or capacity in gpm of a farm water system, the daily requirements for the animals should be pumped during a two-hour period. Therefore, the total gallons required should be divided by 120 minutes.
For example, assume a farm has 50 milking cows, 30 dry cows and 400 chickens. The milk house contains 3 water-using fixtures and the farm home contains 10. The water system requirements would be as follows:
50 Milking Cows @ 35 gallons/cow = 1,750 gal.
30 Dry Cows @ 15 gallons/cow = 450 gal.
400 Chickens @ 6 gallons/100 = 24 gal.
Total Usage = 2,224 gal.
Pump capacity for 2-hour period is:
2,224 gallons / 120 minutes 18.6 gpm
Milk house - 3 fixtures 3.0 gpm
Farm house - 10 fixtures 10.0 gpm
Water System Capacity 31.6 gpm
Average Water Consumption for Home Use and Farm Use
- Home Use -
For overall daily consumption, surveys of families of various sizes in different parts of the country indicate 100 gallons per day per person is a very usable average.
Outlet Total Gallons
Per Usage (gpm) Shower 25-60 5
Bathtub 35 5
Lavatory 1-2 4
Toilet (flush) 3-7 4
Kitchen Sink 5
Laundry Tub 7
Washer (automatic) 30-50 5
Dishwasher 10-20 2
Water Softener up to 150 7
Garden Hose (½) 3
Garden Hose (¾) 6
Sprinkler (lawn) 3-7
- Farm Use -
Gallons per day
Horse, mule, steer 12
Dry Cow 15
Milking Cow 35
Fire 20-60 gpm