The picture describes how a simple water filtration system tranforms dirty water into potable drinking water.
Overall, the process comprises a number of steps, beginning with the input of water, through some gravity-fed filtering stages, and ending with the dispensation of clean drinking water.
At the beginning of the process, unclean water is poured into the elevated plastic barrel, which features a removable lid for easy access. This water then percolates downwards through three distinct filtering layers. First, a layer of sand removes larger impurities, after which a charcoal layer absorbs organic contaminants in the water, before a gravel layer provides further filtration to support for the sand and charcoal above.
The process continues with the filtered water being bumped by a pipe at the base of the barrel into the lower storage drum, which has a sealed lid in order to ensure cleanliness. Once the purified water is collected, a tap fitted to the bottom of this drum allows the drinkable water to pour out for convenient dispensing.