It is important to know the yield of a well to determine if it can produce the peak and total demands required. The actual yield of a well is the volume of water that can be produced continuously, without depleting or pumping the well dry. If the yield of the well is not as much or more than the peak demand required, stored water must be utilized.
A well that only makes 1 GPM can supply 1440 gallons per day, which is enough water for 4 average houses. That is considering 75 gallons per day per person, or 300 gallons per day for a family of four. However, the peak demand will determine the maximum gallons per minute (or GPM) that needs to be supplied by the pump.
Domestic Size Systems
A well with 6" casing will store about 1.5 gallons of water per foot. If there is 100' of water in the well, this is about 150 gallons of stored water that can be used before the well runs out of water. 150 gallons of water stored in the well, will allow a peak demand of 14 GPM for a little over 10 minutes. It will then take 150 minutes for the well to completely recover at a recharge rate of 1 GPM. A single house requiring 14 GPM peak can be supplied with a one pump system and no storage tank, even if the yield and recovery rate of the well is only 1 GPM, as long as the well itself has sufficient storage.
If the well does not have sufficient storage to supply peak demands, a storage tank and booster pump must be utilized. The size of a storage tank must be large enough to supply peak demands for about 10 minutes. However, a margin of safety would require a storage tank than can supply 2 or 3 times the 10 minute peak demands.
Some storage tank/booster pump systems have a means of switching back and forth between the well pump and booster pump. Usually the well pump comes on first to supply water directly to the house. When the well is depleted, the system switches to the storage tank and booster pump. When the storage tank is empty, the well has had time to recharge, and the system switches back to being supplied directly from the well pump. This system allows use of the storage in the well, and requires a smaller storage tank to meat peak demands.
In larger systems, such as a case where four, 3 bedroom houses are supplied by one water system, a peak demand of 56 GPM could be required. If the well cannot supply 56 GPM, then a two pump system with a storage tank would be needed to supply these high peak demands. A 1,000 gallon storage tank could supply 56 GPM peak demands for up to 17 minutes. A pump and pump control system that can supply 56 GPM, and still safely supply as little as 2 GPM, would be needed to draw water from the storage tank to supply the houses as needed. The well pump can then run 24 hours a day if needed, to maintain sufficient water in the storage tank. The lower the yield of the well, the larger the storage tank should be, to provide a margin of safety.
Water in a well usually does not require disinfection. If the well is sealed properly, it should not allow contamination to enter the well. A well is a cool and dark place that does not promote contamination. However, an above ground storage tank may need periodic disinfection. The water quality, temperature, amount of light, and other things determine the amount of disinfection needed. Some storage tanks may only need chlorine occasionally, and disinfection can be done manually. Others may need automatic and continuous disinfection. This can be done with a chlorine injection pump that comes on when the well pump is running, and adds chlorine proportionally to the amount of water being produced.
Storage tanks are vented to atmosphere, and do not supply pressure. A booster pump is needed to draw water from a storage tank and supply pressure as needed. See Booster Pumps.