I can't believe it took me so long, but today I celebrated Independence Day by sticking a bucket in our shower.
Then I showered. The bucket caught about a gallon of water (it was a short shower).
By my calculations, considering that I shower once a day (generally), and that I travel some and shower away from home a not-insignificant amount, I believe this here bucket will spare about 300 gallons a year from the city water treatment plant.
For good measure, I stuck a high-tech basin in the bathroom sink. Washing my hands fills it about halfway. Washing my face fills it completely. Then it's dumped into the bucket.
I bet we could conservatively call that another 30 gallons a year. Of course, 2 people live here and we have my partner's water usage to consider... so we're up to about 660 gallons per year (or 2,500 liters to the rest of the world). That's more than 12 gallons per week, out to our garden beds.
How many flowers do you reckon that would water?
...and why did it take me so long to stick a bucket in the shower?