I have replaced the wall lights in an upstairs room in my house. The
new wall lights need to be earthed. Fortunately the supply is via a
twin and earth cable where the earth was shortened and taped up.

I have enough leeway to use the earth in the supply cable, so my
question related to where to earth these lights to.

In the loft I have water tanks with copper pipe down as far as the
ground floor stop cock where the pipes go out of sight.

Should I get an earth strap and earth these lights to the incoming
water supply pipe, or do the regulations / best practice say I should
do something else.

Many thanks

Phil