Why didn't the government build a giant reservoir to collect water? | Why Guy Walt Gray Why didn't the government build a giant reservoir to collect water when we weren't in drought? | Why Guy Replay Video UP NEXT Today's Why Guy question comes from Adam Lwin on Facebook, who asks "why didn't the government build a giant reservoir to collect water when it was good? Now we are in a drought again? Billions on high speed rail that's not going anywhere." Adam, short answer, all the best dam sites in the state are taken. They were all built in the 1940s, 50s and 60s when we needed dams to prevent catastrophic local flooding.