Water is another fertile source of disease, many organic and inorganic impurities making their way into it. It is to the former that its unhealthfulness is generally due. Nearly all water from the earth contains some mineral ingredients, few of which are harmful, some of which are healthful. The waters of many mineral springs serve as remedies for serious disorders of the system. The chief source of water pollution lies in organic impurities, which are carried through the soil from cesspools, manure heaps, and similar sources into wells, or are emptied by sewers into the rivers from which many cities now derive their drinking water.

The lack of sufficient water may also be a cause of disease. The person and clothes are not properly washed, houses and streets are dirty, and the sewers become clogged with filth. As a result there is a general lower state of health of the community, and typhoid fever and diarrhoea may be prevalent.

Vegetable Impurities.

Peaty water, in the absence of a better supply, may be used without much harm, but if the amount of solid matter is great it may even produce diarrhoea. Under this head we must include water containing germs, for although they generally get into the water from the excretions of animals, yet, as we know, they are vegetable in nature. Here we shall meet with the most dangerous kinds of water, causing many fatal epidemics.

Cholera.

Chief among these is cholera, whose germs are now thought to be conveyed only by water. The great epidemic at Hamburg in 1892, was traced to sewage water from cholera patients getting into the river Elbe, which supplies the city with water. The constant outbreaks of cholera which occur amongst the Mecca pilgrims every year are due to the fact that they wash in and drink out of the same wells, thus leading to an enormous mortality. This frequently, perhaps almost wholly, comes from a like distribution of the bacterial germs of the disease by water. Typhoid fever has been traced to this cause in numerous instances. This was the case at Over Darwen in 1874, when a drain containing the excreta of a typhoid patient was blocked, and its contents got in the main pipe of the water supply. As a result, out of a population of 22,000 there were 2,035 cases of typhoid fever and 104 deaths. In Bangor, in 1882, there occurred an epidemic of typhoid fever, affecting 540 persons out of a population of 10,000, of whom 42 died. This was found to be caused by the excreta of a single typhoid patient getting into a small stream which discharged into the river supplying the town with water.

How People Drink Sewage

Diphtheria

Diphtheria is probably conveyed and caused by impure water, but this is not yet absolutely proved. Dysentery is well known in tropical countries to be caused by impure water, as was proved by an outbreak at Cape Coast Castle, where it was caused by the passage of sewage into one of the drinking tanks. Diarrhoea has been caused in epidemic form by impure water, as was shown in the old Salford jail, where the untrapped overflow pipe from a cistern of drinking water communicated with a sewer, and the water had thus absorbed sewer gas, and probably germs.

Mineral Impurities.

A moderate degree of hardness is not harmful, but if the hardness is great dyspepsia and constipation may result. Goitre seems to be due to the presence of magnesium limestone in the drinking water, but this is disputed by some. Iron salts cause dyspepsia, constipation, and headache. Lead salts are especially dangerous, causing colic, paralysis, kidney disease, and sometimes death. These symptoms may occur when the amount of lead does not exceed one-tenth grain per gallon.