I want to attach a washing machine to my apartment's water supply.

The washing machine is simple and has one inlet and no internal heater. The apartment has both hot and cold water.

I plan to attach some extra pipes via T connectors after the cut-off valves which connect a faucet to the hot and cold pipes. I plan to mix the water using something like this two-inlet valve.

The question: do I need to add back flow / check valves to prevent the flow from hot pipe to cold, or vice versa? If I do, what kind of valves these should be?

Update: this device looks purpose-built for that.

  • 1
    The valve you have linked to is not correct for what you want. That valve is for ONE water supply source IN and two lines OUT. Can you post a photo of the water supply lines you want to connect to.
    – Alaska Man
    Commented May 19, 2020 at 18:15

1 Answer 1


One way to accomplish this is; You can add one Inline spring check valve to each supply line.

After the check valves you can tee the hot and cold together with one 1/2" copper pipe out into a 1/4 turn valve and then to the correct threaded piece to accept the washer supply hose.

The check valves will prevent water from one pipe from pushing into the other.

To regulate the temp of the water you could use 1/4 turn valves BEFORE each of the check valves and close them partially to adjust the temp of the water.

Or just plumb in mixing valve made for the job of mixing and not allowing back flow. I have seen shower mixing valves used for washing machine supply in older homes.

  • The idea of a mixing valve is beautiful! Do all mixing valves prevent back flow, or should I look for some specific keyword?
    – 9000
    Commented May 20, 2020 at 4:15

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