1. (1) General Requirements.

   The distribution system shall be designed to ensure adequate flow and that minimum water pressures as required in R309-105-9 exist at all points within the distribution system.

2. (2) Peak Instantaneous Demand for Indoor Water Use.

   1. (a) Large or complex water systems may determine peak instantaneous demand using hydraulic modeling. The hydraulic model must either apply an instantaneous peaking factor to account for peak instantaneous demand or use actual peak instantaneous water flow data.

   2. (b) Alternatively, the peak instantaneous demand for a single pipeline shall be calculated for indoor use using the following equation:

      Q = 10.8 x N0.64

      where N equals the total number of ERC's, and Q equals the total flow (gpm) delivered to the total connections served by that pipeline.

   3. (c) For Recreational Vehicle Parks, the peak instantaneous flow for indoor use shall be based on the following:

      TABLE 510-6

      Peak Instantaneous Demand for Indoor Water Use for

      Recreational Vehicle Parks

      Number of Connections Formula

      0 to 59 Q = 4N

      60 to 239 Q = 80 + 20N0.5

      240 or greater Q = 1.6N

      NOTES FOR TABLE 510-6:

      Q is total peak instantaneous demand (gpm). N is the

      maximum number of connections. However, if the only water use

      is via service buildings, the peak instantaneous demand shall

      be calculated for the number of plumbing fixture units as

      presented in the state-adopted plumbing code.

   4. (d) For small non-community water systems, the peak instantaneous demand for indoor water use shall be calculated on a per-building basis for the number of plumbing fixture units as presented in the state-adopted plumbing code.

3. (3) Peak Instantaneous Demand for Irrigation Use.

   Peak instantaneous demand for irrigation use is given in Table 510-7. The procedure for determining the map zone and irrigated acreage for using Table 510-7 is outlined in R309-510-7(3).

   TABLE 510-7

   Peak Instantaneous Demand for Irrigation Use

   Map Zone Peak Instantaneous Demand

   (gpm/irrigated acre)

   1 4.52

   2 5.60

   3 6.78

   4 7.92

   5 9.04

   6 9.80

4. (4) Fire Flow.

   1. (a) Distribution systems shall be designed to deliver needed fire flow if fire flow is required by the local fire code official or if fire hydrants intended for fire flow are provided. The distribution system shall be sized to provide minimum pressures as required by R309-105-9 to all points in the distribution system when needed fire flows are imposed during peak day demand in the distribution system.
   2. (b) The water system shall consult with the local fire code official regarding needed fire flow in the area under consideration. The fire flow information shall be provided to the Division during the plan review process.
   3. (c) If direction from the local fire code official is not available, the water system shall use Appendix B of the International Fire Code, 2015 edition, for guidance. Unless otherwise approved by the local fire code official, the fire flow and fire flow duration shall not be less than 1,000 gallons per minute for 60 minutes.

KEY: drinking water, minimum sizing, water conservation

Date of Last Change: July 15, 2015

Notice of Continuation: February 10, 2025

Authorizing, and Implemented or Interpreted Law: 19-4-104