House and Home Part 1 - Washing the dishes

So, let's lighten up today and look at something a little more domestic and quotidian. Dishwashing.
You can't get much more domestic and quotidian than doing the dishes.
Always one concerned to be doing the right thing, it occurred to me to check up on whether it is more environmentally friendly to use a dishwasher or to wash up by hand.
As a product of frugal Middle England, I have always religiously washed up in the sink and the big white box which takes up lots of room in our kitchen gets used once in a blue moon, usually when we have guests or after a dinner party. It always annoys me that you have to check each item on unloading for encrusted food and missed areas, but that's another matter entirely.
From my research, a dishwasher apparently uses anywhere "between 9 and 15 gallons" of (very) hot water for a full load (hands up: who remembers gallons?), depending on the age and efficiency of the machine, much less than the 20 gallons required for hand-washing an equivalent load. Machine-drying in the dishwasher clearly requires a lot more electricity than air drying on a rack, but I failed to find any reliable figures for that.
My immediate reaction was: hold on, that can't be right. So, I checked how much I tend to use myself. Having finally located something denominated in gallons, it turns out that an average daily wash in our household uses all of 2-2½ gallons.
Now, as I say, I am frugal by birthright and by nature. I tend to half-fill a washing-up bowl in the sink, add detergent and some of the dishes, and rinse each batch by running a small amount of hot water over the dishes and into the bowl, thus keeping the washing water hot at the same time.
By the end of the wash, the 2-gallon bowl is more or less full of water, sometimes overflowing a little into the sink if there are a lot of dishes. Drying overnight on a rack (with the overflow on a tea-towel) costs nothing. Bribing my daughter to put the dishes away costs 25¢.
We are a family of just three, and I wash up just once a day, and I can see that a family of four or five would use more water. But how anyone could use 20 gallons I have no idea.
I think I will just follow my instincts on this one.