Like the ones in the photo below. The britina/pur/ge filters that are located at the bottom of the fridge that you just push a button and they pop out, or on some you can turn them and they will come right out. From what I'm reading, there are some that are inline inside the fridge as well.
From what I'm reading, they filter out asbestos, mercury, lindane, atrazine, toxaphene, lead, microbial cysts, cryptosporidium (which is resistantant to disinfection), heavy metals, class I and II particulates, chlorine induced by-products like total trihalomethanes, industrial pollutants, pharmaceuticals found in H2O, . Filters around 750 gallons of water per year. All of course depending on the make/model/size etc.
I figure in a disaster situation or where you need somewhat sterile type water (fast without boiling water), then you could pop one of these out, filter through some water and use.