The automatic inlet of cold water to the hot water system from the main house tank or other source is controlled by a ball valve, which is so fixed as to allow the water to rise no more than an inch above the bottom of the tank, thus leaving the remainder of the space clear for expansion.
The best known of these depressions, Ngami, lies to the north-west and is the central point of an inland water system apparently in process of drying up. To the north-east and connected with Ngami by the Botletle river, is the great Makari-Kari salt pan, which also drains a vast extent of territory, receiving in the rainy season a large volume of water.
Muller, on the other hand, rendering Kreislauf, explains it of the Euphrates water system as a whole, thought of as encompassing Naharin.
The water system of the province comprises a few small rivers (now largely canalized) in the high lands in the east, and the vast network of canals, waterways and lakes of the whole north and west.