LAS VEGAS or Los Angeles would love to have Berlin’s problem: too much water. In the Spree valley, the water table has risen in places to just 2.5 metres below ground level. With most cellars in Berlin between two and three metres deep, that means wet basements, water damage and mold. Some 200,000 people, out of Berlin’s total of 3.4m, live in the worst-hit areas (see map).The puzzle is why, since Berlin is booming, the groundwater is rising at all. The last time it was a magnet for people on such a scale was during the interwar years, when the city’s population was larger than it is today. Water levels then fell as people, factories, breweries and tanneries all tapped into groundwater supplies. It hit an all-time low in the 1930s when Hitler was pumping water for his megalomaniacal projects.After 1945, when industry all but halted, the water level began rising. But it fell again after West Berlin recovered in the Wirtschaftswunder (economic miracle) of 1950s, and because the communists kept prices artificially low and East Berliners used water greedily. But then came unification in 1990. The Ossis…