As the country becomes more settled, ponds are more and more likely to become contaminated and hence unfit for a water-supply, and this possibility must be taken into account in planning for a water-supply. It would be most shortsighted to carry a long line of pipe from a house to a pond several miles away, only to have the pond made unfit for use within a few years by the growth of the community around the pond. The possibility of cooeperation ought not to be overlooked, however. It is quite possible that half a dozen householders might be so located with respect to each other and to a pond that an arrangement could be made whereby the owner of a small pond would agree to fence it around and dedicate it to the purposes of a water-supply, doing this as his share. The others might then well afford to pipe the water to one house after another, including that of the owner of the pond. Water from a pond or lake has one great advantage over water from a brook, namely, that contaminating substances in the pond settle out, so that pond water, especially if the pond is deep, is always of much better quality than running water. For this same reason, water taken from a reservoir on a stream is much better water than that in the stream above the reservoir indicates, and pollution is much less to be feared where the reservoir exists. _Pressure for water-supplies._ The value of a high pressure in the water-pipes of a house has been much overestimated. For a number of years the water-supply in the writer's residence came from a tank in the attic, the pressure in the bath-room being not more than ten feet, and while the water flowing through a three fourths inch pipe was noticeably slow, it was not so slow as to discredit the supply. A height or head of twenty feet above the highest fixture in the house would be better and ought to be secured whenever possible. This head is obtained by having the source of supply higher than the highest fixture, not merely the twenty feet mentioned, but also an additional height necessary to offset the frictional losses caused by the running water. The loss from this source in case of fire supply has already been referred to, but for purely domestic supplies the loss is appreciable. The maximum rate as already indicated is not more than 7000 gallons per day, whereas the fire rate both for single houses and for a small hamlet is about a million gallons a day. For the lower rate, as well as for rates one half and twice this rate, the friction loss in vertical feet per 100 feet run in small pipes is shown in the following table:-- TABLE X. SHOWING LOSS OF HEAD BY FRICTION, FOR DIFFERENT QUANTITIES OF FLOW, AND IN DIFFERENT SIZES OF PIPES