In the UK the technique is known as digging a Gipsy well. It is mostly used as a means of filtering the turbidity and debris from the water. It DOES NOT render the water safe to drink nor will it desalinate sea water. It is also used in situation where there is no visable water source but there are strong indications of presence of water. That generally means in an arid or semi-arid enviroment. You dig the hole, as deep as possible and then cover it to prevent evaporation. Repeat as many times a you are able. You should, if it fills "quickly" disgard the first fill. The only practical ways to desalinate brackish water is by evaporation, either by boilng it and condensing the steam, or by the sunlight and poly bag solar still techniques . Either method is marginal but better than nothing.