Earlier quoted context omitted.
"Our reservoirs are empty. Why would another reservoir help up?" A serious question? More water in reserve = more water in reserve. If you fill 4 glasses with water now, and then then EBMUD turns the water off for the rest of the day due to a broken main (I know EBMUD really well), you'll have 4 more glasses of water to drink than you would have, otherwise. Simple math, really.
Building more reservoirs doesn't mean there's more water in reserve, it just means there's more space to store water.
We're storing a teeny tiny fraction of all the water that goes through the system.