the morning. Reportedly, some locals had attempted to repair leaks in the dam before it completely failed. On 12 March 252 dams were inspected and it was discovered that six embankment dams had shallow cracks on their crests. The reservoir at one concrete gravity dam suffered a small non-serious slope failure. All damaged dams are functioning with no problems. Four dams within the quake area were unreachable. When the roads clear, experts will be dispatched to conduct further investigations. In the immediate aftermath of the calamity, at least 1.5 million households were reported to have lost access to water supplies. By 21 March 2011, this number fell to 1.04 million. Electricity According to the Japanese trade ministry, around 4.4 million households served by Tōhoku Electric Power (TEP) in northeastern Japan were left without electricity. Several nuclear and conventional power plants went offline, reducing the Tokyo Electric Power Company's (TEPCO) total capacity by 21 GW. Rolling blackouts began on 14 March due to power shortages caused by the earthquake. TEPCO, which normally provides approximately 40 GW of electricity, announced that it could only provide about 30 GW, because 40% of the electricity used in the greater Tokyo area was supplied by reactors in the Niigata and Fukushima prefectures. The reactors at the Fukushima Daiichi and Fukushima Dai-ni plants were automatically taken offline when the first earthquake occurred and sustained major damage from the earthquake and subsequent tsunami. Rolling blackouts of approximately three hours were experienced throughout April and May while TEPCO scrambled to find a temporary power solution. The blackouts affected Tokyo, Kanagawa, Eastern Shizuoka, Yamanashi, Chiba, Ibaraki, Saitama, Tochigi, and Gunma prefectures. Voluntary reductions in electricity use by consumers in the Kanto area helped reduce the predicted frequency and duration of the blackouts. By 21 March 2011, the number of households in the north without electricity fell to 242,927. Tōhoku Electric Power was not able to provide the Kanto region with additional power because TEP's power plants were also damaged in the earthquake. Kansai Electric Power Company (Kepco) could not share electricity, because its system operated at 60 hertz, whereas TEPCO and TEP operate their systems at 50 hertz; the disparity is due to early industrial and infrastructure development in the 1880s that left Japan without a unified national power grid. Two substations, one in Shizuoka Prefecture and one in Nagano Prefecture, were able to convert between frequencies and transfer