The Katadyn Gravidyn Drip Filter is the ideal solution for water filtration for groups or for extended periods.  There's no pumping, just let gravity do the work and you've got about 1 gallon of filtered water per hour.

The Gravidyn uses three 0.2 micron ceramic depth filters for extreme filtration.  It's effective against all harmful bacteria and parasites such as Cryptosporidium and Giardia.  Each element also contains granular activated carbon which acts as an absorbant for certain chemicals such as pesticides, also reducing any odor or bad taste. 

The filter is made in two sections.  The top section contains the filter elements, while the bottom acts as a catch and reservoir for your filtered water making it easy to get whenever you need it.  The Gravidyn also boasts a HUGE capacity, up to 39,000 gallons on the supplied elements.  The ceramic elements are also field cleanable should they begin to clog from filtering very turbid water.   Three elements are supplied along with a cleaning pad and gauge to measure filter wear.