maintaining lawns, imo, is ensuring they are kept mowed and neat - NOT watering. watering grass is a wasteful exercise when water is already in short supply. provided the grass is dying off naturally and not from you parking vehicles on it, i would fight it. if their expectation is to have it watered, i would put it to them that they supply water tanks or grey water systems to facilitate this as it is wasteful and not required

as to the rest of the gardens - yeah, it's fair to keep them alive and watered within reason. if they are elaborate gardens, they should be ensuring someone is there to prune them correctly on a semi-regular basis (if we rented this house out, we'd pay for someone to maintain the roses every year so that they were pruned properly)