Lyn, a couple of thoughts here and forgive me if I repeat someone else's suggestions, I skimmed through a few of the posts above.
Have you pruned the top growth of your trees at all? The less leaves the tree has to support, the less water it needs.
Also, about that lawn that is under the maple tree, the grass is using water that the tree would get if you could remove the grass. When the rains return (some day, let's hope!) you can easily replace the lawn, but not the tree. Maybe spread a thin layer of mulch or compost over the grass to kill most of it off? Better yet, spread newspaper, cardboard or something to smother the grass plants. Don't forget that the trees have roots out usually as far as the reach of the branches, so maybe burying soaker hoses under thick mulch around the drip line would water the perimeter roots better?
Here in FL we have sand, sand, sand so when the weather's dry and sunny it dries very quickly. UF research has shown that early morning watering when the air and soil temperature is lowest, and breeze is least is the most efficient time of day to water as it minimizes evaporation. Can you put in a timer or two to turn on the water at 5am or so?
