You could always turn the top inch of soil (careful not to go very deep) and THEN water. It will help get the water down into the root zone.
BTW it sounds like your having a hard time keeping them watered, but a south faceing hilltop that gets sun all day is THE best place you could have planted your grow. I bet its a lot of work, but you will be VERY happy you put them there come harvest. Keep it up man..you should be half way done and starting to see flowers now (or very soon).