In my copy of the WRAS Water Regulations Guide it menitions the
"water undertaker" a lot but does not seem to identify who this is.
You have to inform the "water undertaker" for example if you install
something from a list of items that includes, for example, a water
softener.

i don't think the "water undertaker" is the local building control
becuase things liek installing a combi boiler does not have to be
informed to the undertaker and I think it does to BC.

Robert