I have always heard that but I never understood how that's possible. I filled a rice bowl with water and reuse that same water to wet all the dirty dishes before rubbing, then rinse with cold running water from the tap.

The majority of the energy used in dishwasher is from heating up the water. If you wash with cold water, you are using less energy than the dish washer.

From earlier comments, it appears that a dishwasher will consume at least 2.5 gals per cycle. No way does hand washing use 5 to 7.5 gallons of water per wash. Being a single guy, I stopped using my dish washer for the several dishes I dirty every day and always hand wash. I first put in about an inch of hot water and wash the utensils. I turn on the hot water again to rinse the utensils with the cast off water going back into the wash sink. The rinse sink is used only to hold the clean, rinsed dishes. I continue on washing each item this way (from cleanest to dirtiest). Most of the time when I'm done the sink isn't half-full.

Because I can only use water cool enough to put my hands in, the dishes are not as clean as what a dishwasher can do, but, again, no way does a single wash consume 5+ gallons.

Do you have a source for that? I've always heard it, but... I've also watched a lot of people wash dishes in ways that waste lots of water unnecessarily.

I'd be curious how the study was conducted, and if they have video of the study participants washing their dishes.