Sometimes, when a shallow dug well does not furnish the required quantity of water, the amount of water can be increased by driving pipe wells down into water strata below the one from which the dug well takes its supply, so that water will rise to the strata penetrated by the dug well. This has been done to increase the public supplies at Addison and Homer in New York State. Unfortunately, much uncertainty exists in the matter of the yield of driven wells, and an individual undertakes a deep well usually with great reluctance on account of the expense involved and the uncertainty of successful results. In level ground, conditions are not likely to vary in the same valley, so that if one well is proved successful, the probabilities are that wells in the vicinity will be equally so, and yet, at some places, the contrary has proved to be true. One may estimate the cost of putting down four-inch driven wells as approximately one dollar per foot besides the cost of the pipe, which will be about fifty cents per foot. The cost of one-and-one-half-inch pipe would be considerably less than fifty cents, the cost of driving varying not so much with the size of the pipe as with the soil conditions. The writer recently paid ninety dollars for driving two one-and-one-half-inch wells to a depth of about one hundred feet, the above cost including that of the pipe; the soil conditions, however, were very favorable. In Ithaca the cost of driving one-and-one-quarter-inch pipe is fifteen cents per lineal foot up to about fifty feet deep with the cost of the pipe fifteen cents per foot additional. Below fifty feet deep the cost increases, since the labor and time required for pulling up the pipe is largely increased, and at the same time the rate at which the pipe will drive is notably diminished. The question of pumping from wells will be considered in a later chapter, together with methods of construction and operation. _Springs._ Springs should be the most natural method of securing water-supply for a detached house, since no expense is involved except that of piping the water to the building. In Europe, spring water-supplies have been greatly developed in furnishing water for large cities. Vienna, for example, with its population of nearly two millions, obtains its water-supply from springs in the Alps mountains, and many smaller cities do likewise.