"Lobster" wrote in message
news
SNIP

Anyway, I'm now considering biting the bullet and installing a 'proper'
blue
MDPE pipe, which means digging up the drive and considerable
expense/hassle,
and so not something to be undertaken lightly, and unless I'm 100% sure
it's
going to make a decent difference to the water flow at the two shower
heads.
So my question is, is there a way of finding out? How can I be certain
that
the bottle-neck is caused by the length of water pipe under the drive, or
elsewhere (eg the yards of 15mm pipework inside the house, or whether the
water pressure out in the road is not that great in the first place?)


"If" the main under the road is of adequate size then a drop in flow must be
related to your supply branch pipework. However if you and your neighbours
are being supplied by a somewhat smaller street main then a pressure loss
due in part to the resistance of the street main will affect you "and" your
close neighbours. Try asking your next door neighbour if turning on your
taps can be noticed in the flow rate available in their house too. A
practical test may be needed.
The most likely scenario is the loss occurs in your suply branch but if you
are at the end of a street or live in a terrace then the shared supply may
be the problem.