is that system of supply where the rain-water drainage of elevated water-sheds is gathered in natural or artificial storage basins, and conveyed through conduits by gravitation to the point of supply. The important points entering into the consideration of this method are: 1. Character of water; present and future contamination. 2. Water-shed; present and future requirements for quantity and availability, with proper knowledge of the geology of the surrounding country. 3. Rain-fall, absorption and evaporation. 4. Elevation and distance of source. 5. Route of conduit. 6. Cost of construction. The practical objections to the system are: 1. Contamination of source by surface drainage of cultivated lands; pollution of feeding streams, or growth of vegetation. 2. Necessity for large impounding reservoirs for storage of water during rainy seasons, requiring immense puddled walls, whose stability is questioned. 3. The uncertainty of dependence on the requisite rain-fall, and liability of short supply, or a possibility of water-famine. 4. The large expenditure at the outstart for construction of supply that must be ample for future demands. Surface waters from calcareous cultivated lands are polluted with but a moderate amount of organic matter; but, as some of this matter is almost always of animal origin, they are always undesirable, and may at any time become dangerous for domestic use. If necessity compels their use, great care ought to be taken to secure their efficient filtration before they are delivered to consumers. This affords some, though by no means complete, protection from the propagation of zymotic disease through the agency of such waters. They are generally very hard, and, unless artificially softened, occasion a great waste of soap when used for washing. Of all the waters of this description, those which flow from the surface, or from the drains of sewage farms, are generally most impure, because the time during which the foul sewage is exposed to the purifying action of plant and soil is reduced to a minimum. Surface water from non-calcareous soil is generally soft but usually turbid and subject to animal contamination. Such water should always be carefully filtered. ANALYSIS OF LAND DRAINAGE WATER FROM SEWAGE FARMS (PARTS BY WEIGHT OF 100,000 PARTS).