As the old saying goes, “Someone with one watch knows what time it is, someone with two watches is never sure.” Water accounting is fundamental to water management, but is not easy.  But any accounting is more difficult and expensive if it is less organized.  To illustrate this point, let’s look at estimates of one of the largest, most important, and “easiest” to measure flows in California: the annual pumped quantity of California’s State Water Project (SWP) Banks Pumping Plant (Banks) in the Delta for the years 2006 through 2010.