What is this mystery pipe?

[Emma Walsh]

I am renovating an old mining terrace in the Welsh valleys (uk) and I have come across a mystery, I have my mains water supply to my property and a stopcock near the front door that cuts off all water to the property. However I also have blue pipe coming from the floor in my kitchen, also with a stopcock, which i assumed was the cold water supply to the kitchen,but it is not.
We have just had the plumbing redone and the plumber assumed as I had that this was the cold water. The stopcock attached stops the water cooing in to this pipe not out?
So we have turned it to closed and it has had no effect on the water supply to the property.
Can anyone help solve this mystery??

 

[ShaunCorbs]

Out to an outside tap or out buildings ?

 

[snowhead]

If not outside, as Shaun, Have any of your terrace neighbours lost thier water supply?