Dr. Natterer records that the sample, which was clear, tasted slightly alkaline, and contained very distinct traces of nitrites and nitrates, free carbon dioxide, free ammonia, and organic matter. During my stay of four days at Halaib in May 1908, I drank regularly of the local well-water; I found it very hard, and though the Arabs seemed to like it, its action on myself was so strongly aperient that I sent into the mountains to Bir Frukit for purer supplies for use on the long march to Port Sudan.
As a rule, it is the magnesium salts which are the most harmful constituents, the sulphate giving a strong purgative character to the water. Such salts are naturally present in greatest quantity where the rocks are gypseous, as for instance along the coast to the south of Halaib, where the wells of Ti Kureitra, sunk in gypsum and lined with blocks of selenite, yield water of so purgative a character that all my Arabs who drank of it became violently ill. In districts where the rocks are of very basic igneous types, such as gabbros and serpentines, the salt-content may also be fairly high. Water from diorite country is somewhat better, that from granite better still, and that from sandstone best of all. There are practically no wells in clayey strata within the region here treated of, but Bir Qoleib, which is on the road from Daraw at about two days’ journey east of the Nile, is sunk at the foot of a clayey scarp, and the water, when I partook of it in 1907, was clouded with clayey matter so finely divided as to be unfilterable through a Berkefeld filter even under strong pressure, while the physiological action of the water was to produce very marked constipation. Wells near the sea coast are liable to be very salty from infiltration of sea water. As a rule, the very salt wells, such as Bir Murra, Bir Muelih, Bir Shalatein, and Ti Kureitra, are used only by camels and sheep. When the Arabs have to drink purgative water for lack of other supplies, they often mix milk with it, and I have found it wise to imitate them in this respect, with liberal addition of brandy in some cases.
Wells are generally named after the wadi in which they occur, e.g., Bir Abu Hashim is the well in Wadi Abu Hashim. A bitter well is often called Bir Murra.[118] A deep well is called Sararat by the Bisharin, e.g., Bir Sararat Seyet is the deep well in Wadi Seyet.
Questions are often asked as to whether it is not possible to increase the available water supplies by sinking fresh wells. Where it is a question of sinking a new well in the middle of a long waterless stretch, or where the object is to sink a fresh well near an existing salty one in order to obtain a drinkable quality of water (and these are the two most usual cases), success cannot be predicted with any certainty, even in the most likely looking spots. We must remember that though the present Arabs may be lazy, the older tenants of the desert were more active. We have only to look at the old mining centres to see this. The probability is that the old miners were just as much worried by the scarcity of water as we are to-day, and with the cheap convict labour then available we may rest assured that every attempt was made to increase the supply. And it is not probable that the Arabs will have allowed to fall into disuse any existing well on an otherwise waterless road, so that it is likely that most of the wells in the wadis remote from the mountains are at spots specially favourable which have been discovered by a laborious process of trial and error. Confirmation of this view is supplied by the failure of new wells sunk at considerable cost in likely-looking places, as for instance at Abu Rahal, where a well carried down to over sixty metres’ depth failed to find water. Where modern wells have obtained water, they have usually been sunk near to or on the site of existing wells, as for instance near the temple of Seti I and at the different mining centres; in these cases it has sometimes been found possible to increase the supply by going deeper. And with regard to obtaining sweet water by sinking new wells near to old salty ones, no success can be hoped for if the saltiness is due to a general salt-content in the surrounding rocks; the Mines Department well in Wadi Mellaha[119] yielded no better water than the Arab well in the same wadi, because the alluvium everywhere in the wadi contains abundance of salt. In some cases, it may be, the promotion of a more rapid flow would lead to a slight lessening in the salinity; but if a well becomes salt merely by evaporation resulting from stagnation, that very fact shows that it is not much used by the ordinary traveller; and moreover the rate of flow of the underground water is not as a rule sufficiently rapid to yield large supplies, even from wide excavations.
In the south parts of the country, where the rainfall is greater, it is possible, nay, even likely, that many new wells could be sunk with success; but in these localities existing wells are more abundant and the necessity for new wells does not arise.
Rock Basins (Galts).
The typical rock basin, called a galt[120] by the Arabs, is a smooth-sided cavity in the rocky floor of a steep gorge draining a large mass of high hills. Galts are generally difficult of access, being situated in the higher parts of very stony wadis, so that one has to tramp often over miles of steeply rising stony ground to reach them. Galts abound in all high mountain-masses in South-Eastern Egypt, and furnish the greater portion of the water supply of the population. The capacity of galts varies very much; some hold millions of litres. Often there is a chain of successive galts at intervals along the length of a gorge, and after rain the whole series is filled, while much overflows and runs to waste. The origin of the rocky basins is generally due to pot-holing action on a large scale. Galts may occur in rocks of any hard type, but are most commonly met with in eruptive rocks. Sandstone galts never remain long full, owing to the permeable nature of the rocks. The large Galt el Aguz near Gebel Um Harba, which from the inscriptions near it was evidently known and used in Ptolemaic times, is in sandstone, receiving in fact the superficial run-off from the same high mass of sandstone hills as furnish the collecting area for feeding by percolation and underground flow the adjacent springs of Bir Abraq and Abu Saafa; but the galt is seldom full for more than a month or two, while the springs are constant.
The water supply of galts depends firstly on the rainfall of the district; secondly, on the existing drainage system; thirdly, on the presence and size of eroded basins along the lines of drainage; fourthly, on the nature of the rocks forming the basin, and, lastly, on the degree of exposure to evaporation. The rainfall in the Eastern Desert is often very local. A series of galts full one year may be dry the next, while those of another area may show a reverse state of things. The drainage system most favourable to galts is one formed by the union of long narrow steep-sided gullies into a single gorge. The presence of basins is conditioned by the steepness of the drainage and the hardness of the rocky floor; if the rocks are soft or much crushed, galts are very unlikely to occur. Again, if the basin is formed of permeable though hard rock, there will be rapid loss by infiltration. Evaporation is generally far less rapid at galts than in open country, because being in narrow gorges galts only receive the sun’s rays for a few hours of the day, and are, moreover, sheltered from winds.
The quality of galt water varies very much with the interval since rainfall and with the nature of the rocks. Sandstone galts are very pure, because of their short life and the siliceous nature of the rock. Serpentine and diorite galts contain magnesium and other salts, and as the loss by evaporation continues the water may become somewhat bitter and purgative by concentration of these saline constituents, though galts never suffer to the extent that some wells do in this respect.
A galt is frequently accompanied by a small spring (megal or megwel); the galt represents the run-off, while the spring receives the percolating water. Thus for months after a galt is empty it may in some cases be possible to obtain water in small quantity by scooping out sand-filled rock cavities close to the basin.