It is further highly important to protect the well from drifting leaves and dust, and also from being used by strangers and passers-by. This is most easily effected by building a well-house over the mouth of the well, provided with a door, for even if this is not kept always locked, it at least serves as an intimation to outsiders that the well is not public property, which will probably be generally respected. As the well-house may be of the simplest material and construction, the cost of one need be no bar to the adoption of the plan; for the shelter will always be of small dimensions, and can be built with walls of sun-dried brick and a thatched roof, or even of grass screens throughout. A single metal vessel and rope should be provided, which should never be removed from the well-house, and no other vessel should be permitted to be lowered into the well on any pretence; for the practice of each person carrying about his own drinking vessel and string provides the mechanism whereby cholera is carried from one place to another in the majority of outbreaks of that disease in India. If possible, only a single servant should be employed to draw water, and he should be provided with a padlock and instructed to keep the door locked. Very probably the door will often be left open, but it is something gained if it be locked for some hours in the day, as the fact of finding the door even sometimes locked will serve to show outsiders that the use of the well by them is regarded as a trespass. Provided that the entry of leaves and other even more objectionable matters be prevented in this way, a well should require but little attention, though it may be useful to occasionally purify it, especially if it has been out of use for some time, by treatment with permanganate of potash in manner described below. Where a well is persistently foul, it may be taken as certain that this is due to prolonged neglect and insufficient cleansing; for when, as is usually the case, no attempt is made to guard a well, so much dust and rubbish of all sorts gain admission that it requires to be emptied and thoroughly cleaned out, down to the soil in which it is excavated, at least once a year, and the expense of doing this will be found to be at least as great as the construction of a well-house of inexpensive materials. When the water of a well has been obviously offensive, the actual soil at the bottom of the well should be dug out for two or three feet, and fresh, clean river sand substituted. After the well has refilled, it should be treated once or twice with permanganate, and the water will then usually be found to be restored to good condition.