Water is one of the most important of our foods, it is a necessity of life to us. Our bodies contain about two-thirds of their weight of water, and the blood contains 79 per cent of it. Water is continually being separated from the blood, and got rid of by the excretory organs, and has to be replaced If an individual is kept without water he soon becomes reduced to i state of muscular debility, with the greatest possible prostration, the excretory organs begin to lose their power, and he ultimately dies in extreme pain.

The next thing to the use of water as a food is its use for cooking and washing-the domestic uses of water. It is found that if a water supply is deficient in quantity many evils ensue. Food is cooked with the same water twice; people do not wash themselves as much as they should, or in the same water twice, the action of the skin is impaired, the other excretory organs overworked, and so a state of body is produced in which people are very liable to diseases of various kinds.

Besides this, water is used for a variety of public purposes: for cleansing the streets, flushing the sewers, etc., and the absence of water for these uses in a town makes the spread of disease much more easy.

Professor Rankine laid down a rule that thirty-five gallons was the greatest amount necessary per head per day, but that thirty gallons was to be considered a sufficient supply. Many towns have not anything like this amount, but vary from six gallons upwards.

In ancient times and in some modern cities a very much larger supply was and is considered necessary. The supply of ancient Rome is calculated at 300 gallons per head. The ancient Romans attached extreme importance to having sufficient water always at hand. In all Roman camps in this country, if you search you will find that they never pitched a camp for military purposes, except' in a place where they could get water either close by or within the camp, and almost always within the camp.

A very remarkable example occurred to me a short time ago. A friend of mine took me up to see a Roman camp at the top of a sandstone hill It puzzled us to think how the Romans ever got water at the top of that porous hilL We were, however, strolling about, when suddenly I saw half-a-dozen rushes, and that was quite enough to show that there was water. A pocket of clay was there which prevented the water from going down farther, and, no doubt, there was a well at that spot to supply the camp.

We require water of a certain quality for drinking purposes, but we do not require it of the same quality for the other uses.

We might, if it were convenient, have two supplies, one for drinking and another for washing the streets, flushing the sewers, for baths, and so on. If not, all the water supplied must be fit to drink.

In the first place water for drinking should be clear, it should be transparent and colourless,, it should contain no suspended matters in it, and deposit no sediment on standing. It should be aerated, and it should be fresh to the taste, neither salt nor sweet, and should have no smell. Now, if a water does not conform to all these characteristics, it may be said to be water not fit for drinking purposes, but it may, on the other hand, conform to them all and yet not be fit for drinking, for many waters in wells are highly aerated, very sparkling and clear, but are totally unfit to drink, and that is because water may contain matters in solution, and, practically speaking, it always contains matters in solution of one kind or another. It may, in the first place, contain mineral salts in solution to a very considerable extent, sometimes to such an extent as to form petrifying streams or springs.

Water contains most frequently salts of lime, and the salt which is most common and found in the greatest quantities is carbonate of lime. This carbonate of lime, originally in the form of chalk or limestone, is dissolved in the water by means of carbonic acid, which is derived, in the case of rain water, from the air through which the rain passes. The other salts found are sulphate and nitrate of lime, chloride of calcium, chloride of sodium or common salt, and others.in smaller quantities, such as salts of magnesia and salts of iron.

From the presence of these mineral salts, either in large or small quantities, waters are divided into two classes-viz., hard and soft. Water that contains a large quantity of mineral salts is hard, and water that contains a small quantity soft.

Besides mineral salts, water may contain in solution, as well as in suspension, organic matters, and among the matters it contains in suspension there may be live creatures, plants and animals.

What is the effect upon health of drinking water containing these various substances ? In the first place, waters containing suspended matters are not wholesome waters to drink. They are liable to derange the digestive organs. That is the case whether they contain suspended mineral matters, or whether they contain animal or vegetable matters.

Waters containing a large quantity of mineral salts have been said to aid in the production of calculous disorders, but with regard to waters containing moderate quantities of mineral salts, the evidence goes to show that they are not deleterious to health. It is found that the death-rate in towns supplied with moderately hard water, does not materially differ from the death-rate in a series of towns supplied with soft water. It appears, roughly speaking, that there is no great harm in drinking moderately hard water, if the hardness in the water is due to carbonate of lime, but if the hardness is due to magnesian salts, or other salts of lime than the carbonate, then it is liable to be deleterious, especially to people who are not accustomed to drink that particular kind of water. And when persons go into a country where the water contains sulphate of lime, as when the water comes from rocks in which sulphate of lime is abundant, for instance around Paris, then they suffer from derangements of the digestive apparatus. Water containing magnesian salts has a special effect which I shall mention shortly.