The Golden State: Where & How to Live, Secure, Visit, Enjoy and Thrive in California
How To Design And Install Plumbing
The factor of probable demand or the amount of water a distribution system is called upon to produce in any period of a 24-hour day arises from the problem of simultaneous use of plumbing fixtures and is largely a guess on the part of the designer. He may be guided by the type and design of the building, the purpose for which it is to be used, the number of people who are to use it, and many other undetermined elements. Some statistical information is available, but it is still exceedingly vague and may only be used in correlation with practical trade experience. The probable demand is not likely to be more than 25 per cent of the maximum demand, especially for average size buildings of the residential type, and this figure may be used with safety to establish the size of a water service.
Method of Determining Demand. To show how the unit system may be applied in determining the maximum and probable demands of a water supply system, a five-fixture residence is given as an example. Using the unit values of the fixtures, as explained in Chapter VI, the following compilation results:
The total of 92^ gallons represents the maximum demand. As consumption of this volume of water is unlikely, the amount may be reduced materially. As previously indicated, the probable demand for this type of building would not be more than 25 per cent, so it is safe to use 25 per cent of 921/2 gallons, or approximately 23 gallons of water a minute.
There may be some question on the part of the reader as to the correctness of using a value of 6 units for a water closet, because a closet of the flush tank type discharges much less than 45 gallons per minute. As was previously indicated, the size of the water service as well as that of the distribution system is largely to be assumed. No method of calculation is entirely dependable. To justify the use of flush valve closets, no mention of lawn sprinklers has been made. The average residence is provided with two. Should the building be provided with tank closets instead of flush valve closets, then it is advisable to determine maximum demand on this basis.
A value of 2 units (15 gallons) of water may be used for flush tank water closets, but added to the maximum demand to offset this change must be added the discharge of two lawn sprinklers, which amounts approximately to 4 units or 30 gallons of water.
