In many places huge dams retain river water and rainwater ​ — a measure that has proved somewhat effective, even though reservoirs in arid areas may lose about 10 percent of their water through evaporation.
Paljudes paikades aitavad jõe - ja vihmavett sulustada tammid ning see on osutunud küllaltki tõhusaks, kuigi kuivades piirkondades võib sellest veest aurustuda umbes 10 protsenti.