[stephen.b1]

could this be the answer to a trolly or a backpack

http://www.wired.co.uk/photos/wired-things/2009-09/01/design-for-good/aquaduct-bike.aspx

Aquaduct is a simultaneous water-transportation and filtration vehicle, created for the developing world by five engineers based at Ideo in Palo Alto, CA. The bicycle has a 20-gallon storage tank at the back, from which a pedal-powered pump draws water via a filter into a front-wheel-mounted container. Brian Mason, a mechanical engineer on the project, says: "When we roll this out it won't necessarily be a big blue bike. It could be a trailer that attaches to existing bikes, or people could replace parts in their bikes."

[Gleaming windows]

There was soemthing pretty much the same on Dragons Den to this about 2 years ago, for purifying water in desert regions where family members have access to water which isnt necessarily clean but is available.

The trolley is taken to the water source and filled, on the way back the rotation of the wheels drives the water through a filtration system theoretically purifying the water, so people dont have to walk half as far to get their water or otherwise inappropriate water can be used which would be unsuitable without purification.