How do poor people filter their water?

Can anyone tell me a brand & model of a battery powered WATER pump (filter) for a fish tank/aquarium?

• There is a question (from someone else) asking if you can get a battery water filter and lots of people said yes... that didn't really help, as I can't actually locate one, so can someone who has one give details of what it is so I can look for it? I don't have an aquarium, so please no answers about other ways I might keep fish alive or the cost of running the filter on batteries, I am using the filter as part of a larger electronics project to do something else completely, and it must run on batteries (portable ones!! Not a car battery invertor) to achieve it. I am not looking for an air pump, I am looking for a WATER pump, an external or in-tank type filter. A pond filter is no good, it needs to be a tube to tube filter, not a submersible.

• Answer:

  How long do you want it to run for? You could modify a small 12v pump to run off some normal batteries, for an hour or so. Then the batteries are dead. A car sized battery will maybe run it for a couple days. I dont know of any usefull water pump that will run off small batteries, the pump would just kill the batteries too quickly to be of any use. Maybe search for solar powered garden fountains or water pumps, or 12v systems used in RVs etc would be the closest thing I can think of. Ian