The orange (on the foliage?) will be willow rust releasing its spores. Its a parasitic fungus. Too late do anything about it now as it has completed its life cycle. Clear up all leaves in autumn to reduce re infection next year. You could spray with a preventative fungicide next March/April and again in May.

The second part to your question. No, you won't be giving the willow too much water. The rootstock used is Salix viminalis (Basket Willow/Osier) and grows along river banks in saturated soils so this has absolutely nothing to do with the problem.