I don't know how long the showers took today, but I rearanged the order of starting and managed to only have the water run for a few seconds where I wasn't washing anyone (of the 4 of us)
I know you are thinking that is obvious, but I think showers clean better than baths, and DD can't sit in a bath with shampoo or soap in it (bad for girl parts) and UE can't be wondering around he has to be in the tub (9month old baby) and at some point the bathroom has to get bleached, and I have to fix hair shortly after the two older ones get out (curly, style when wet), and showers are not just about getting clean they are also body parts lessons (ankle, toes, ect) water physics (floats or sinks?) and fun time.....today I did it with about as little water as I think will ever occur
you really don't need all the details, but for non parents just know it isn't as easy as you think!