vsop wrote:

I'm told that my new acid loving Blueberries (in containers) should be
watered only with rainwater......but in these dry conditions I no longer
have any !
My tap water is neutral ph, so, could I not make suitable non-limey liquid
by throwing a handful of ericaceous compost in a bucketful of tapwater and
letting it "stew" for a couple of days.
Would this have any detrimental effects on the plants ?
Does anyone see any problems, or can offer alternative advice.

Mine get tapwater when rainwater is in short supply and don't seem to
mind all that much. Add some Miracid feed to it if in any doubt.

The insides of your kettle is a good guide to how hard the water is. If
you have to descale it every month or it blows fuses you have extremely
hard water (like Belgium). If it is clean inside then your water is very
soft - most places are somewhere inbetween. Water engineers tend to add
a trace of lime to very soft water to dicourage it from corroding pipes.

As long as most of their water is soft rainwater the odd bit of tapwater
will do them a lot less harm than prolonged drought.

Regards,
Martin Brown