Complex sentence: They purify water by passing the water through pores in ceramic that are smaller than bacteria or virus, so they cannot pass through the filter and will remain within it until it is cleaned or replaced.
Split into simpler sentences: They purify water by passing the water through pores in ceramic. The pores of the Ceramic are smaller than the bacteria or virus, so they cannot pass through the filter and will remain in the filter until it is cleaned or replaced.