New Hampshire Code of Administrative Rules
Env - Department of Environmental Services
Subtitle Env-Dw - Drinking Water Programs
Chapter Env-Dw 400 - PUBLIC WATER SYSTEM CLASSIFICATION AND DESIGN
Part Env-Dw 405 - DESIGN STANDARDS FOR SMALL COMMUNITY WATER SYSTEMS
Section Env-Dw 405.32 - Distribution System

Universal Citation: NH Admin Rules Env-Dw 405.32

Current through Register No. 13, March 27, 2025

(a) All small community water supply systems and those NTNC water systems important to public health as specified in Env-Dw 405 .02(g) shall comply with this section.

(b) The water distribution piping system shall be capable of passing peak flow without excessive frictional loss. At peak flow, pressure at the sill elevation of each lot or unit shall be at least 20 psi. This determination shall be made at peak flow and when the atmospheric water storage tank is in a one-half empty condition. Consideration shall be given to possible future expansion in the sizing and layout of the proposed water distribution piping system.

(1) Where operational pressure is anticipated to be less than 30 psi, the service line shall be oversized so as to reduce frictional losses. The water system owner shall inform each potential service customer of this low pressure before each unit is constructed;

(2) Individual booster pumps to increase water pressure shall not be used on the service customer's premises to maintain the required 20 psi minimum working pressure; and

(3) Maximum system pressure shall be 100 psi. Any portion of the water distribution piping system where pressure is expected to exceed 100 psi shall have pressure reducing valves installed on each individual water service line or on the water main to maintain pressure at less than 100 psi. Any bypass line around a water main pressure reducer shall also have a pressure reducer. The water system shall maintain all pressure reducing devices.

(d) The water distribution piping shall be so valved as to allow isolation of major sections of the water distribution piping system for repairs while still providing service to most of the water system. The spacing for on-line gate valves installed on water mains shall not exceed every 1,500 feet. Gate valves shall be provided at all intersecting pipes.

(e) Blow-offs shall be installed to allow flushing of the water distribution piping system near the ends of the water mains. The size of the blow-off shall be such as to permit high velocities, at least 2.5 feet per second, to be developed in the water distribution piping.

(f) Where possible, dead-end piping shall not be used. Near the temporary end of a water main, a gate valve shall be installed to allow future piping extension without shutting down the system or jeopardizing the health of existing consumers.

(g) Water distribution piping shall be bedded in sand or other appropriate material with a minimum cover of not less than 5 feet for year-round systems.

(h) If a water main and sewer pipe are to be installed adjacent to one another, a minimum horizontal separation of 10 feet shall be maintained.

(i) When conditions prevent 10 feet of separation, the following shall be considered by the water system:

(1) Where other utilities or obstacles, not including bedrock, prevent such separation, a waiver shall be granted to allow location of the sewer pipe not less than 3 feet from a water main horizontally, provided that the water main is in a separate trench or on an undisturbed earth shelf located on one side of the sewer and at an elevation so the bottom of the water main is at least 18 inches above the top of the sewer pipe;

(2) If a water main must cross a sewer pipe, the water main shall cross above the sewer pipe with not less than 18 inches of clear separation;

(3) Water piping shall cross under sewer piping only when this is demonstrated to be unavoidable and only when granted by specific waiver. Special construction, including use of ductile iron water and sewer pipe, no pipe joints within 9 feet of the crossing points, and minimum 18 inches clearance shall be required; and

(4) Technical criteria supporting a waiver of sewer pipe and water main separation criteria include:

a. The topography of the area; and

b. The number of utility interferences.

(j) Piping and valving material and installation techniques shall conform with the appropriate AWWA specification, in accordance with Env-Dw 407, for that type of piping material where such specification exists. Where such specification does not exist for the size pipe included in the system design, the minimum pressure rating for piping shall be 200 psi and the piping shall meet the manufacturing requirements of the American Society of Testing and Materials (ASTM) specification 2241, available as noted in Appendix B .

(k) Other utilities including but not limited to natural gas, storm drainage, electric, telephone, steam and cable television, shall not be installed within 3 feet of water mains.

(l) All buried non-metallic piping shall be backfilled with an effective metal tracing element located above the pipe approximately 6 inches below the finished grade.

(m) On-line gate valves and house service shut-offs shall be equipped with cast iron gate box extensions. Gate valve boxes shall have cast iron covers clearly marked by the word "water" or other appropriate water supply marking and shall be installed flush with the finished grade.

(n) Rigid connections shall not be used to construct or repair water distribution piping systems.

(See Revision Note at part heading for Env-Dw 405) #10612, eff 6-1-14

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