I've been googling this for ages, but I am getting conflicting reports as to what sort of head is really necessary. Some are arguing for upwards 10 or 20 metres (30 or 60 foot) of head, and then I read a New Zealander talking about 0.9m (3 feet) of head being sufficient and a common practice over there. I get that if one wants the usual levels of pressure (that those with pumps / mains water are accustomed to) you're probably going to need quite a lot of head, but suppose you just want enough head to operate a low pressure shower - will something like 0.9m actually work? And what if you additionally need to get that water through some kind of a heater - probably solar or wood combustion? Does that complicate things?