Drinking water is essential. People need to drink at least two litres of water a day, and twice that on hot days. Apart from that, you can just get by with five litres/person/day for all other needs. Seven litres is more comfortable but you still need to be frugal. Given some care, ten litres/person/day is fine. Some campers use plastic or metal jerry cans but humping 20-25 kg of water is pointless when you need only small amounts.
One or two 50-55 litre tanks fit under most camping trailers, but a growing trend is to have only one, and to use 12-15 litre containers of pure water for cooking and drinking. These are available cheaply from most fuel stations and supermarkets. Their use removes concern about tank water not being sterile – and there is no need for filtering.
If tank water is used for drinking, install a coarse filter (pre-pump) to trap sand and grit, then (post-pump) add a 10-micron paper filter, then a one-micron paper filter. These fix the main health concerns: of Giardia (from faeces) and Cryptosporidium. Filters must be changed yearly.
There is a vague standard for the housings, but some accept only individual maker’s (costly) filters. Stay with the former.
Hand or foot pumps are slow and tedious but, because of this, they usefully self-limit water usage. Electric pumps are more convenient and cost only a little more.
Centrifugal pumps are simple, quiet and cheap but only pressurise. They cannot not suck water so must always be below water level.
Diaphragm pumps both suck and push. They work well if used regularly but not otherwise.
Most draw 4-7 amps (at 12 volts) and, depending on hose size and length, deliver about 7-10 litres a minute.
Shurflo has a diaphragm pump that supplies water at constant pressure.