Which particular ericaceous plants are you asking about and how 'hard' is your tap water? Generally I'd say 'yes' but fill a bucket or container and let stand for a couple of days.

That's interesting MG....I am curious. We are ok here because we have no lime in our water of course, but in Lincs where I grew up and London of course, they have so much lime in the water. Would that not be damaging to Rhodys etc? If you let it stand for a couple of days, does the lime sink to the bottom?

I 'did' ask how 'hard' Theherbgardeners tap water was Karensusan. We never need to water our rhododendrons, nature does it for us and ideally this is how they 'should' be watered. But if THG has his or her rhododendrons in containers and is in an area of drought then they may have to water with tap water. Letting the water sit for a couple of days wont get rid of any lime but will get rid of chorine and the like.

You are certainly better off saving enough rain water in butts to see you through dry periods although this can be difficult. I once killed all my blueberries off by having to use tap water when we had no rain for months. Letting the tap water stand will not get rid of dissolved lime which is what ericaceous plants hate.

But if it is a choice on watering with tap water or not watering at all...

Yes, I understand. Bottled water perhaps! ;)

Bottled water is often no better. Distilled or reverse osmosis water is fine but is very expensive.

Extremely expensive. Perhaps the solution is to not try and grow ericaceous plants if you live in an area where there is lime in the soil. I know I personally couldn't be bothered with all the challenges.

When the weather is really dry, and rhododendrons and azaleas and hydrangeas, etc., all lime-haters, will die if they don't get SOMETHING, we resort to watering with tap-water, (we live in an extremely hard water area) but from time to time we dose the plant with something such as Sequestrine, so that the plants can assimilate the iron needed for chlorophyll production. It's enough to keep all our ericaceous plants going and healthy.

Good thinking Gattina. The active ingredient of Sequestrine is Ferrous (iron) sulphate so if you find this in its pure form you can save a few bob and not pay for trade names. Just for info and clearly not trying to teach Gattina what she already knows.

Gattina needs all the instruction she can get, Sarra, and anything she DOES know she's learnt from others on this site! So pass it all on along. :-)

Many thanks to Moongrower, Karensusan6, Sarraceniac and Gattina for your welcome comments and suggestions. The ericaceous plants that I have are one azalea and one hydrangea that I have been given. I have planted both in pots in ericaceous compost and to date have watered both with rain-water but am rapidly running out of it. Your suggestion about Sequestrone, Gattina, is very helpful and I shall certainly try this anyway, especially with the hydrangea as it is a pink one that I am trying to change to blue.

I really appreciate all of your answers and again my thanks.

You hydrangea does not need rain water or ericaceous compost it will do just fine in any soil - trying to turn it blue has the potential to produce something that is neither pink nor blue but a washed out shade of both. (I remember my father trying to do so when I was a child)

Thanks for the warning Moongrower.