SOURCES OF WATER SUPPLY.—All our drinking water is obtained in the first instance, by a natural process of distillation on a large scale. The sun is constantly causing evaporation from sea and land. The vapour produced, being condensed by a lower temperature, returns to the earth as snow, dew or rain. All these natural products have been at times utilised as sources of drinking water. 1. =Dew= has on rare occasions been utilised at sea by hanging out fleeces of wool at night and wringing them out in the morning. A much better plan is— 2. The =Distillation of Sea-water=. This can easily be managed now that steam power is so largely used. It has even been employed on land, when it was necessary temporarily to continue the use of water derived from an impure source. The first part distilled should always be rejected, as it is always impure. Distilled water is “flat” in taste, owing to its containing no dissolved gases. It can be aërated by letting it drop a considerable distance from one cask into another, through small openings in the upper one, and by filtration through charcoal. Non-aërated water is not easily absorbed into the circulation, and occasionally causes illness. 3. The utility of =Melted Snow and Ice is= obviously very limited. Moreover, its use is not free from danger if the ice is derived from contaminated water. Outbreaks of enteric fever have been traced in the United States to the taking of ice obtained from impure water. 4. =Rain-water= is a much more important source of water supply, and after passing through the soil it constitutes the chief part of the water we drink. The term, however, is properly restricted to the water collected immediately after its descent from roofs, etc. Its purity depends on three conditions—the character of the air it passes through, the cleanliness of and absence of lead from the channels through which it runs, and the condition of the water-butts in which it is stored. Rain-water is soft; in fact, too soft to be pleasant to the palate. In passing through the air, it carries with it a certain proportion of its constituents; in towns especially ammonia, soot, etc.; near the sea, it generally contains some salt; and being soft and having dissolved oxygen from the air, it dissolves an appreciable amount of lead from roofs or gutters. The Rivers Pollution Commissioners found that out of eight samples of stored rain-water only one was fit to drink. They came to the conclusion that rain-water, collected from the roofs of houses and stored in underground tanks, is “often polluted to a dangerous extent by excrementitious matters, and is rarely of sufficiently good quality to be used for domestic purposes with safety.” Also, that in Great Britain, and more particularly in England, we shall “look in vain to the atmosphere for a supply of water pure enough for dietetic purposes.”