In some localities where the water (though it may be chlorinated and bacteria-free) is dark and turbid and full of the finest sediment, the usual sand or quartz (even with the tiniest of spaces between the grains) cannot prevent this hyper-fine sediment passing through into the filter. In order to catch this impure water with its fine sediment alum is often introduced into the filter to coagulate the fine sediment (as you have seen the white of an egg coagulate coffee grounds) and permits it in the “flock” to be caught as it passes through the interstices of the filter bed. Here you can easily see why you must be careful to give the filter manufacturer a graphic description of your water supply. Then, too, the installed filter, just described may be rendered useless if by any means the pipes in the home become contaminated. There are some filters on the market (this caution is for the unfiltered community) which only strain. Those fitted with paper, cloth, cotton, etc., are fine in their places, but you must know their places. One filter, for example, is said to be very speedy. However, in this case (this filter is attached to the faucet) you are admonished to let the water run for about half a minute, because, as the water ran through before, the collection of germs must be given a chance to flow out. In this filter the water flows in at one end through bone char and quartz and the next time it is used the current is reversed and flows back through the filter bed, self-washing but carrying with it the bacteria collected on its last passage. Therefore, if you forget to let the water run for a time, you may get your stomach full of more potent germs than if you used the ordinary water with its occasional bacteria. Good filters in the last analysis spell “safety first” wherever they may be. For despite municipal intervention accidents will happen, and even though the trouble be corrected in a short time, fifteen minutes can prove a real menace. There is one filter just coming to our markets, made in Germany, which has been tried and tested and found good. It is affixed to the water supply (direct, not in cellar) and accomplishes filtration by the process of passage of water through a paper-like fabric of disks ¹⁄₄″ thick. These disks keep water absolutely sterile in the laboratory for 17 days but the makers, rightly, will only guarantee them for 48 hours in order to obviate danger to their promises, through the accidents which may happen. The test under German scrutiny proved that typhoid germs were rendered nil for 17 days and try as they might could not force their way through the disks. This is a good certificate of good conduct. Sewage for example during the war was rendered harmless as drinking material by the means of this filter disk, so it is claimed. Filtering, unlike sterilizing, does not take the life out of water or make it readily absorb odors and flavors.