Since 1885 thousands of filters have been patented. Years ago the smallest and most unreliable maker would put a filter on the market and promise immunity from death and let it go at that, because folks are anxious to be saved. To-day not many more than six filters are really sold with a guarantee by reliable firms backing them. Why? Because most of these filters were cheap and flimsy, did nothing but strain water and strain their point as well. These small manufacturers would spring into being one day and sink into oblivion the next. The filters, if they did filter (not strain, only), would become breeding nests for bacteria. Physicians feared and forbade them. The filters on the market to-day are in varying degrees reliable, depending greatly on their functions, on the amount of care and wear, and how they are used. For example, coarse gravel as a medium through which to purify water might be good to take out bits of sediment--big bits--but it would not act on the bacteria. In general, the materials used in filters through which the water must pass to be purified are: sand, quartz, charcoal, cloth, paper, etc. Another class of filters passes the water through a bougis or candle made of unglazed porcelain (Kaolin), natural stone, artificial stone, asbestos, diatomaceous earth, etc. The pores through which the water flows catch the bacteria and sediment. With this list before you you must ask yourself if you need only a strainer. Is the water free from bacilli? Have you a municipal chlorinating plant or filter plant? If so, any good filter will do to strain out suspended matter; but if you are very anxious to have perfect water you cannot go wrong by having a filter which will catch bacteria which may have accidental entry, in any community whatever. If you know you have dirty water and no municipal plant you cannot be too careful as to what you use in rendering safe the water from well, stream or any other source. The most reliable faucet filter is the diatomaceous earthen candle type which is simply cleaned by brushing off its soft surface and boiling occasionally to kill furtive bacteria. The great drawback to this type of filter is that it is not a reformer and cannot force the user to keep it clean. Therefore it is up to the user, and as its agent told the writer, “Filter use in a city like New York is a matter of temperament. Some people enjoy caring for a filter in order to make a splendid water supply fool-proof, others dislike the care and do not mind the slight risk in any city water supply or the discoloration that is often inherent.” Filters, whether installed or attached to faucets, are built to fit the occasion.