Water Needs

Water Needs

Assume now that the well had adequate capacity to meet reasonable water needs. Pump selection then depends on two basic criteria: (a) the water needs of the customer, expressed in terms of both total demand and peak demand; and (b) the pressure requirements of the system. These criteria cannot be considered separately in sizing a pump. They must be taken together.

Following is the procedure for determining water needs in various applications.

Residential Installations:

In sizing water systems for homes, total demand is not normally the governing criterion. Studies of domestic water usage put the average daily requirements of a household at 50-75 gpd per person, with houses in the luxury class using perhaps as much as 100-150 gpd. Even at this higher figure, daily consumption for a family of five would come to only 750 gpd. Translated into average flow rate, this comes to about half a gallon per minute, which almost any well can produce and any pump deliver.

Rather than total demand, peak demand is what counts in residential jobs. A simple but accurate method for determining normal peak demand is to count all of the water outlets or fixtures in the house and allow 1 gpm for each outlet. Thus, in a modest vacation home there would be a bathroom with water closet, tub or shower and lavatory (3 outlets), a kitchen sink (1 outlet) and possibly an outdoor hose bib (1 outlet).

Using the formula of 1 gpm per outlet, safe method of determining the best pressure setting is to go by the fixture or outlet of greatest elevation and farthest from the pump. When water flows through this fixture at full capacity, the pressure should be at least 10 psi on the inlet side of the unit. If this is the case, there is almost a 100 percent chance that pressure will be adequate throughout the system.