Gagagran I have 3 large established Hydrangeas which I'd be gutted to lose as they are irreplaceable. I am watering them every evening, and a professional horticulturalist told me that, as tap water contains chemicals and will wash nutrients out of the soil, to feed them plenty of Miraclegro once a week to give them a boost. After a scorching day, one of my Hydrangeas in particular often looks sorry for itself, but perks up overnight with this treatment. Fortunately we haven't had a hosepipe ban here (yet). I give most of the water to the roots but just give a quick spray to the leaves when the sun has set.
This is the one that needs the most TLC but overnight it has recovered.