Ive got a 500 gallon water tank I put in the pack of my truck and the pump I use is one of those sewage pumps with a 4.5 hp honda. If there is a creek nearby I just throw the hose in the water and set up my sprinklers and I can water them with no problem. If your going to use a 15 gal sprayer you better have a very small plot and a lot of time. For me to sufficiently water an area 90' X150' I figured it will take about 2500 gallons of water.