On the electrical side, the pumps linked to earlier in this thread don't seem to draw that much juice, say 1.5kw. If you have a battery / inverter / solar system like we do then running a generator to charge the battery takes about 1.5kw also. Ergo... An 8kw genny would pump water and charge the batteries at the same time with 5kw left for the washing machine or whatever you use to make best use of the genny running time.
BTW we bought a set of fork lift batteries from eBay for £250. 700Ah @24V and they are only 2 years old. Had to bring them from England but still well worth it.