Coastal rain is therefore isotopically different from inland and different again in the mountains. In the process water acquires telltale isotopic 'fingerprints' in different environments, and analysis of a sample, using special instruments, can reveal its 'age', origin and how it got there. Isotope hydrology techniques measure the ratios of a number of other elemental isotopes, i.e., helium, carbon, nitrogen, sulphur and chlorine. Preliminary results in Egypt appear to be promising. It has been ascertained that the shallow Nile aquifer is being replenished by the gigantic Nubian Sandstone aquifer which lies adjacent to it and at a deeper level.
Ongoing studies expect to establish the rate and quantity of replenishment.
The fact that the Nubian Sandstone aquifer contains 'palaeowater' which has not been actively recharged since the last rainy period some 6000 years ago, is not regarded as a problem. This aquifer covers an area of tens of hundreds of square kilometres, and is the largest known aquifer in the world. It is unlikely to be depleted by extraction for the reclaimed land area. The study is expected to determine how much and at what rate Nile aquifer water can be withdrawn without unwanted consequences. The news is mixed for Morocco.