Building a water well rig is easy all you have to do is put your creativity to work.Go to Northerntool.com and take a look at a 13 hp Honda engine, a 8gpm Hydraulic pump, and at 14 gpm low speed high torque hydraulic motor,the engine has to have  1"  shaft with a keyway then you need a pump bracket and so on. This is if you want to build your own hydraulic power unit but you have the option of buying one already set. Hydraulic pumps for drilling application have
to be single stage, 2 stage pumps are for log splitters.You'll need control valve 1 for motor and 1  for hydraulic cylinder to raise mast up and down. But first design what you want and then get to work is better when you have a plan to follow. Hydraulic portable water well rigs work and no need of big trucks to get the water you need.The information above is for a 13 hp hpu producing 1200 psi continuosly and 2000 psi intermitente, plenty of power for your first rig then you can build them any way you want.