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Public Health - Seattle & King County

Installing your new waterline

Before you get started, follow the procedures on "How Do I Get a Homeowner's Permit?"

You must also check with your water supplier to find out what the water pressure is in your area. If the water pressure is more than 80 pounds, you will need to get a pressure reducing valve.

Approved materials for outside waterline
PVC, PE, copper, PEX, PEX-AL-PEX or PE-AL-PE materials are some commonly used approved materials for cold water supply piping outside of a structure. The pipe must have a minimum working pressure of 160 pounds.

Laying outside line
When you are digging the trench for your new waterline, be sure the waterline is 12-inches below the local frost depth, but in no case less than two feet underground. Always call 1-800-424-5555 before you dig.

Approved materials for inside water distribution
The types of material for pipe allowed for your inside water distribution include: CPVC, copper, brass, PEX, PEX-AL-PEX, galvanized malleable iron, galvanized wrought iron and galvanized steel are some commonly used approved materials. Both the hot and the cold water distribution piping inside the structure shall be of the same material.

Measuring for and laying inside line
Use the charts in water supply fixture units (WSFU) and minimum fixture branch pipe sizes for the purpose of sizing the water system. Figure out the number of units for your fixtures. You want to make sure that each fixture is going to receive enough water pressure. Don't forget to size the hot waterline separately from the cold waterline. If your pipe needs to be supported, be sure to do so using the manufacturer's specification. If your project includes a shower or a shower/ tub combination, you have to put in anti-scald valves. Install nail plates where piping is within 1-1/2 inches of the edge of framing members.

Backflow protection
A backflow occurs when an unwanted substance gets into your drinking water while drinking water is being held in your pipes. A "cross connection" is a connection between your water and a possible source of contamination. If your project includes an irrigation sprinkler, a boiler or fire suppression system, you will need to have backflow protection. All hose bibs must have a vacuum breaker or anti-siphon valve on them.

Cold weather protection
Hose bibs must have a frost free shut-off valve or a shut-off valve in a warm wall. All piping exposed to cold weather must be protected from freezing. Disconnect hoses from faucets during cold weather.

Water hammer arrestors
If you are installing a dishwasher or a clothes washer, you must install a water hammer arrestor on the water lines. This is to protect the piping system from hydraulic shock.