I recently bought an under-the-sink drinking water filter, a model from GE, and I got stuck trying to hook it up to the cold water line.

The package came with a simple plastic tee that had a 1/2 inch MIP, a 1/2 inch FIP, and a 1/4 inch connection for the tubing that goes to the filter. My trouble is that I don't have any 1/2 inch connections after the shut-off valve -- the connections there are 3/8 inch compression connections (I'm slowly learning the difference between the various fitting types).

I've been trying to find fittings that would let me adapt the plastic fitting that came with the filter for my situation, something like the following:

shut-off -> 3/8 fem comp x 1/2 mip -> plastic tee -> 1/2 tip x 3/8 male comp -> water line to existing fixture

But I can't seem to find anything like a 3/8" female compression to 1/2" MIP adapter. It also seems like having more joints in a plumbing system might cause problems, so using the fewest fittings possible sounds like a good idea.

Is there a better way to do this? Some way of avoiding the included plastic tee?

So, to restate my problem, how can I accomplish the following:

shut-off, 3/8" m comp -> 3/8" f comp x 3/8" m comp -> 3/8" f comp fixture line
                         1/4" quick connect tube
  • FYI: MIP = Male Iron Pipe, FIP = Female Iron Pipe
    – Tester101
    Commented Feb 11, 2013 at 20:41

1 Answer 1


You're going to need to get a 3/8" x 3/8" x 1/4" brass tee, like this one from Home Depot.

enter image description here

Then you'll simply screw the tee onto the male end of the shutoff valve (where the cold water supply line should currently be attached). Attach the supply line (that you removed from the shutoff valve) to the male end of the tee. Finish the installation by attaching the tubing to the 1/4" outlet using a compression fitting (Which should be included with either the filter or the tee).

  • The link, picture, and description are all very helpful! My local Home Depot and OSH didn't have anything like that in stock (and I certainly looked...). Commented Feb 11, 2013 at 21:24
  • I just found this at a plumbing supply place ... or I should say, the plumbing supply place figured it out for me. Also try Amazon under the name Watts female adapter ... good luck
    – user21941
    Commented Jun 5, 2014 at 19:00
  • Déjà vu
    – Tester101
    Commented Jun 6, 2014 at 10:24

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.