Droopy rhododendron

My rhododendrons are in big tubs as my garden soil isn’t suitable. I think they are pretty much pot-bound, as I watered them, but it ran straight through.
Anyway, I bought a bag of ice for each from Tesco, that way the ice melted slowly and the compost absorbed it. They’ve definitely perked up. Unfortunately, the builders had to empty my water butt to move it, so tap water until it re-fills.

I'm afraid mine was tap water.
But of course it could be a different issue anyway.

Probably just the hot weather anyway.

They may prefer rain water?

Mine was droopy a couple of days ago.
I watered it ^thoroughly and it's back to normal now.