You cannot overwater a Salix if it’s planted in the ground … so give it two buckets full of water every other day for the next ten days then two buckets full twice a week until the end of September. Pour tge water gently over the root area so that it soaks right down to the rootball and doesn’t run off the surface.
It might just be that the very hot weather and drying winds have frazzled the leaves … but lots of water won’t harm it and might just save it.
Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.
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Would need a photo though, to give more/suitable advice.
I live in west central Scotland - not where that photo is...
Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.