If the hydrangeas had got to the point of drooping, then the brown leaves were destined before you got water to the roots, and couldn't be stopped. You just left it too long before you watered - you may find more shrivel and drop off. You've not said whether they're in the ground or in pots - if they're in the ground, and they've been in more than two years, the ground must be very dry indeed. I take it you've checked the backs of leaves and all stems for signs of infestation or disease?

Most of them are in the ground but I have one in a pot that a know gets a lot of water. There is no sign of infection or disease. Thanks for your comments.

I only ask about infection/infestation because of where you are - I know its very dry here in the south, but don't know how dry its been where you are.

Whether its been damp enough for those in the ground depends on how long they've been in the ground as much as anything - as for the one in a pot, if the compost dried out, its quite difficult to get it wet enough again - water tends to run straight through if the compost is bone dry.