Water System Design Manual
Equation 6-1: Individual Source Capacity
( )( )
Vj = Total volume for source "j" over a specified period of time (gallons per specified time
Qj = Delivery rate of source (gallons per unit time)
= Time that flow (Q
was delivered from source "j" over a specified period of time
(minutes, days, or years)
Engineers should base the design flow-rate (Qj)
for each source on any limiting factor that might
restrict the peak-flow rate (such as well or aquifer capacity, installed pumping capacity, intertie
capacity, treatment limitations, or legal limitations).
After determining the source capacity, the engineer can establish the production capability for
the water system based on the time that each respective source can be, or is, used within a longer
period (over a day, month, or year). For example, a pump may be restricted to operate for only a
designated amount of time each day, or a treatment plant may produce water for only certain
periods each day. In addition, some sources included in the water system's annual water-demand
determinations may operate only seasonally.
Note: To determine maximum source-production capacity, it is clear that pumping for the full
1,440 minutes a day will provide for the maximum level of service (ERUs). However, even
though this allows service for a maximum number of ERUs, it may not be practical to operate
source pumps continually for 24 hours, even during peak-demand periods. Whenever there is
concern over pump protection under a full 24-hour operation, it may be wise to plan for pump
operation less than 1,440 minutes per day. Be sure to factor in any reduced pumping times when
determining water system capacity in ERUs.
When engineers know the specific delivery-rate and operation-time of delivery for each source,
they can use Equation 6-2 to determine total source capacity (the total quantity of water available
over a specified time period from all sources).
Equation 6-2: Total Source Capacity
j = individual source designation.
= Total volume of water available to a water system over a specified period of time,
gallons per specified time period