Wells not dug into firm rock had to be lined There is a difference between deep and shallow wells. Shallow wells are much more likely to become contaminated with liquids from sewage that have seeped from pits or broken pipes. In the past this caused major health problems. Deep wells are much safer because the rock is a natural filter and a great depth of rock ensures that all harmful substances will have been trapped before the water reaches the deep wells.

Wells are still widely used, although most are covered and the water pumped out. There is also no need to dig big wells. These were only needed because the well had to be big enough for a person to dig it out. Modern pumped wells are dug by a boring machine (similar to those used for oil wells) and it is about 60cm across.

Pumping is done to add to drinking water supplies and also to give supplies to farmers, breweries and others. In this case the wells (also known as bore holes) are drilled wherever the water is needed, so there is not too much piping needed to get the water from the well to where it is needed.

Not all places have rocks that store water. The continent most lacking in suitable rocks is Africa, which is a shame because, with a large rural population, wells would have been very useful. As it is they can only be dug in a few areas.