just moved into my first new house in 17 years! My old house was a new build and very simple. This new to me house is about the same and had quite alot of basement work done at some point. That's where things start to confuse me. As you can see in the pics below, I have a plumbing quandry.

So here's what I know. The large shutoff in the middle of these runs appears to be the main shutoff. There is no longer a shutoff right out of the concrete and you can see where they removed it.

The bottom run is a 1/2 inch pipe and supplies the spigots BEFORE the softener. The softner then comes into play. The confusing thing is that there's a T there which would seem to be sending un-treated water SOMEWHERE, but I don't know how to tell where!

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  • That valve making the "H" is actually your water softener bypass. That's for if the water softener breaks down. If that's not obvious, you have more to learn about pipe layout. A common use of non-conditioned water is the outdoor faucets. Each of these valves should be cycled annually. If you don't, then 14 years later when you go to use them, they won't seal because they're full of crud. Jan 23, 2020 at 20:46

2 Answers 2


I disagree that you see the main cutoff anywhere here. Keep looking - all those pipes originate from some other inlet to the house.

My guess about the red-handle valve is it's there to allow water flow when the softener tank is "offline". That valve should be closed under normal operation.

I see two "T" joints after the green valve. One has the blue-handle valve on it. So, to trace a bit, do this: 1) turn the red handle off. 2) Do whatever is needed so water can't pass thru the softener assembly. 3) turn the blue handle off.

Now any outlet/tap/ fixture which still gets water flow probably comes from the T-line on the left. Once you've identified those, open the blue-handle valve and see what additional items have water flow. Everything that doesn't have flow at this point probably goes thru the softener leg.

  • My guess is it goes to a water heater... good catch on the red handle. i thought the same thing but you typed faster..
    – JACK
    Jan 23, 2020 at 20:16
  • Original Poster here, yeah that IS the main cutoff! You would expect the main to be right where the street line comes into the basement. NOPE! There was a shutoff there once, but it was REMOVED. The shutoff you see is the best we can come up with for stopping water moving through the house. Jan 24, 2020 at 13:27

This is an idea that I have never tested, but it sounds good in my head... That said...

Get an IR thermometer or another fast-updating method for measuring the temperature of the pipes. Hold the IR thermometer against the unknown pipe and get a good baseline temperature when NO water has been running for hours.

Now, turn on various water sources and see which pipe changes temperature. Water from the street will be a different temp than the water inside in your pipes. There may only be an immediate difference of a few degrees, but once the mystery pipe starts to change temp, you will know what it supplies.

If anyone knows why this would or wouldn't work, feel free to call me out.

  • Could the blue valve line go to an outside faucet that doesn't need soft water and does need to be cut off so it doesn't freeze? (posting my musings as comments to my own question...)
    – JPhi1618
    Jan 23, 2020 at 20:19
  • 2
    It looks like it might be common for only the HOT water to be softened, so the tee before the softener could be for ALL the cold water.
    – JPhi1618
    Jan 23, 2020 at 20:22

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