11/7/5 2 Umbra, Umbra, Umbra,
Girl,
U gotta get to thinking better on this... now let's see, are there typically any tanks near the shower where you can store the water until it can be used (say for flushing solids down the sewer pipe, maybe)?  Consider using gallon milk jugs, filled with the cold shower water, then pour them into the toilet tank right after a flush, or just water the plants.

There are also domestic hot water recirculation pumps that keep the warm water slowly circulating which can save some water and energy in some cases, but be sure to include a night and weekend timer to turn the pump OFF when it is not being used.

With natural gas prices doing a x1.5$ this winter I am using my water heater a la Mexicana, that is I turn it way down after my shower and laundry, then strike it up about an hour before I will need it again.  This limits the standby losses, and I only pay for what I use.  One could argue that since my tank is inside the house, that the lost tank heat goes into heating my house, but I use a set-back thermostat, so that is less the case.  Also the standby flue losses from a hot tank (water and room air) can be significant.  Hot air will gravitate up and outta the house 24/7 unless you install a code-approved automatic flue damper.
Bests,
j'Deen
NRG Engr.

I learned from an unemployed friend to turn the water heater off , except for one hour before a shower.   Amazingly, most people think this wastes heat because "you have to heat that cold water again"... Even a Physics graduate told nme this!
- moral: the unemployed know more about practical thermodynamics than graduates?

[to convince any silly graduates: say, "If I'm going away for 5 years, should I leave the water heater on? How about 5 days?  
- the actual reasoning is this: waste energy is that which escapes from hot water, the hotter the more waste heat escapes  (4th power?)]