Oh how lucky you are to not have frost line to worry about! Here water lines had better be several feet down to work in the winter, or not be froze and broke all to pieces the next summer. Years ago we shanked one through a wide shallow creek, bladed kind of a trench through it with a D6, then used a boot on a ripper shank to put in on in. Usually this creek only runs March-June but there was quite a bit of water in it when it was done. I am sure there is some government outfit that would haul you to jail if you tried it now. Directional boring maybe- sounds cheap ;-) .