Shallow wells made by driving iron tubes with well points into the subsoil water are preferable to dug wells. Use a draw-pump in preference to draw buckets. When a well is sunk through an impervious stratum to tap the larger supply of water in the deeper strata, we obtain a "deep well." Water so secured is usually of great purity, for the impurities have been filtered and strained out by the passage of the water through the soil. Moreover, the nature of the construction of deep wells is such that they are more efficiently protected against contamination, the sides being made impervious by an iron-pipe casing. In some rare cases, even deep wells show pollution due to careless jointing of the lining, or water follows the outside of the well casing until it reaches the deeper water sheet. Deep wells usually yield more water than shallow driven wells, and the supply increases perceptibly when the water level in the well is lowered by pumping. While surface wells draw upon the rainfall percolating in their immediate vicinity, deep wells are supplied by the rainfall from more remote districts. Deep wells are either non-flowing or flowing wells. When the hydrostatic pressure under which the water stands is sufficient to make it flow freely out on the surface or at the mouth of the well, we have a flowing, or true artesian well. _Character of Water From Deep Wells_ Water from deep wells is of a cool and even temperature. It is usually very pure, but in some cases made hard by mineral salts in the water. Sulphur is also at times present, and some wells on the southern Atlantic coast yield water impregnated with sulphur gases, which, however, readily pass off, leaving the water in good condition for all uses. In many cases the water has a taste of iron. No general rule can be quoted as to the exact amount of water which any given well will yield, for this depends upon a number of factors. Increasing the diameter of very deep wells does not seem to have any marked effect in increasing the supply. Thus, a two-foot well gives only from fifteen to thirty per cent more water than a three-inch-pipe well. This rule does not seem to apply to shallow wells of large diameter, for here we find that the yield is about in proportion to the diameter of the well.