Minimum Water Supply Pressure

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Prepared by:  Stephen J. Brown, P.E., Director of Water Resources
Supersedes:   9/16/2010
Adopted by Council:  10/30/14
Effective:  10/30/14 


  1. To establish a minimum water supply pressure to be provided throughout the Town of Cary’s potable water and reclaimed water distribution systems;
  2. To ensure that potable water and reclaimed water distribution system improvements are designed to provide adequate flow and pressure for supply (potable and reclaimed) and fire protection (potable only).


This policy shall apply to the potable water and reclaimed water distribution systems within the Town of Cary’s utility service area, owned and operated by the Town of Cary, for customers billed by the Town of Cary.


The Town shall design and maintain its potable water and reclaimed water distribution facilities such that the following residual water pressures will normally be available throughout the distribution system: 

  1. 40 pounds per square inch (psi) at average day and maximum day demand conditions;
  2. 30 psi at maximum hour demand conditions;
  3. 20 psi at max day demand with maximum applicable fire flow demand (potable only) conditions applied at worst-case location.  Minimum fire flow rates shall be as required by the Town of Cary Standard Specifications and Details; 

to be consistent with North Carolina Department of Environment and Natural Resources (NCDENR) requirements stated in NCAC T15A and other applicable regulations.

This policy is intended to establish minimum conditions.  Higher pressures may in fact be available depending upon the geographical and topographical location in the system.  If pressures higher than the stated minimums are required at a given service location, it shall be the responsibility of the customer to provide the necessary engineering analysis and pressure boosting facilities.

The Town shall develop and maintain computerized hydraulic models of its potable water and reclaimed water distribution systems.  These models will serve as the basis for planning hydraulic performance of the systems.  Model results will be used to predict potable water and reclaimed water pressure availability under the various demand conditions described above.  Designs for new potable water and reclaimed water distribution lines and system appurtenances (storage tanks, valves, etc.) shall provide the above mentioned minimum pressures.  Designers shall provide a design report, including hydraulic analysis results, to show that these conditions are met at all times. 

This policy is not to be viewed as a guarantee of minimum water pressure availability.  Rather it is intended to provide a basis for design of facilities connected to and utilizing the potable water and reclaimed water distribution systems by water customers.  The requirements of this policy are not intended to exempt other policies.  All construction shall meet the current Town Standard Specifications and Details.