I bought a Water2 filter that needs to be connected to the cold water pipe of the kitchen tap. There are only rigid plastic pipes (see photo below), so I won't be able to do it as is and have a few questions:

  1. How can I find out the thread size of these white pipes? Do I need to take them apart to measure them or is there a way to know without? This is in the UK.
  2. Am I right thinking that 2 simple flexible tap connectors such as this one should do the job, as long as I get the right thread diameter ones?
  3. I've also included the sizing bit from the filter installation guide, it comes with a converter but I guess ideally I should buy connectors in sizes so I can install without the converter?

Edit: I just realised I'd need a couple of male-male thread inserts as the tap connectors seem female-female only?

Thanks in advance for your help!


filter installation guide

  • IMHO, the easiest way to figure out thread sizing is to take the part to a store and try it out against the various bits they have there. Once you find the thing it threads to, you can read the packaging to know what size/kind of thread you have and can go from there.
    – FreeMan
    Jan 9 at 13:20
  • @FreeMan that's a good point, though the rest of my family would need to stay without water while I'm at the store because the bit of the pipe to take contains the stopcock so I'd need to turn off the water mains.
    – dain
    Jan 9 at 17:23
  • Sometimes, needs must. You'll probably be without filtered water until you do.
    – FreeMan
    Jan 9 at 18:59

1 Answer 1


I managed to finally finish this job and it was a pain in the backside so I thought I should share what I learnt.

Photo of water filter installed under sink

  • you can't just screw a few of these bits together, each is built around (in this case) the 15mm internal pipe
  • the Speedfit fittings are great, but if you don't know the mechanism (see https://yewtu.be/watch?v=v6kRm3KKCQo) it'll leak
  • copper pipes need couplers properly tightened so you'll need two wrenches that can open wide enough (the IKEA one I had could only do ~20mm which is just about too small) or in my case I didn't want a second one so welcomed a slip joint plier into our family (pictured above)
  • a copper pipe with the straight factory cut will leak, you need the chamfered, smooth end done by the round pipe cutter (thanks https://yewtu.be/watch?v=wzJyIZl2GtE)

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