I’ve never personally painted a car, but I’ve helped; I leave the actual spraying to my brother who’s does it for a living.
As for painting cars at home without a booth and whatnot, honestly, the best results will be gotten if you basically make your own booth; it can be done for about $50 in materials and about a day of work. It only takes a box fan, a few 2x2s/2x4s and a couple rolls of hi-mil vapor barrier plastic. Basically build the box around the car using the 2x2/2x4s to frame the plastic to the cieling of the shop and hold the plastic to the floor, put the fan at one end, and cut a small slit at the other end to allow air in, basically making a horizontal flow booth.
As for the water idea… not good.
It is ALL in the prep work, sanding, priming, sanding, and sanding some more. Then properly mix the paint with reducer/hardener and take your time spraying properly. If you do this you will have a good paintjob with little to no contamination (due to the redneck booth) and not a lot of post-paint sand/buff.