innovatedevelopment.org/2015/06/07/...p-to-produce
The design for the filters used today was developed in 1981, by Dr. Fernando Mazariegos of the Central American Industrial Research Institute (ICAITI) in Guatemala, whose intent was to create low-cost filters, manufactured locally, that would make bacterially contaminated water potable. These filters would thus be available to the “poorest of the poor”.
As water passes through the ceramic container (picture a clay pot you would use for a house plant), bacteria is trapped and the clean water is able to flow through the pores created in the process of cooking the containers in a kiln. The educational video on their website describes the texture of ceramic like a series of layered chain-link fences, which work to prevent a golf ball (bacteria) from making it to the other side.