This is the third year of unusually dry conditions, so reserves where already somewhat low to begin with.
Dams generally store water from excess years to be used in lean ones, but like anything there is major cost benefit analysis going on. Usually, they trade some power generation capacity for water in lean years, but they can't let dams get to low or you risk structural problems.
Suppose you built a standby hover just to store water. Assuming you found a usable location and outside of the direct costs for construction and ~125,600 acres of land. It's going to cost you 791,000 acre-ft/yr * (1 acre-ft ~= 325,851 U.S. gal) = 257 BILLION gallons of water every year just for a standby. Considering water is already in short supply in good years it's just not worth it.
Dams generally store water from excess years to be used in lean ones, but like anything there is major cost benefit analysis going on. Usually, they trade some power generation capacity for water in lean years, but they can't let dams get to low or you risk structural problems.
More importantly, one of the major, but less talked about issues is evaporation. http://pubs.usgs.gov/sir/2006/5252/section2.html
Suppose you built a standby hover just to store water. Assuming you found a usable location and outside of the direct costs for construction and ~125,600 acres of land. It's going to cost you 791,000 acre-ft/yr * (1 acre-ft ~= 325,851 U.S. gal) = 257 BILLION gallons of water every year just for a standby. Considering water is already in short supply in good years it's just not worth it.