To really save energy you could do like beer brewers have done for years - convert a chest freezer into a fridge. The cold air stays in while the door is raised.

http://mtbest.net/chest_fridge.html

Yes, your fridge works easier full than empty.

A better option is to buy a smaller fridge in the first place. Get a fridge that will be full under normal use.

And while you're at it, get a super-efficient one.

I wonder how many times you have to open the door before the energy required to cool the water is less than the energy saved by the refrigerator doing less work each time you do. My guess would be quite a few, since water has a very high specific heat amd thus takes a lot of energy to cool down in the first place. That property (which means the water stays cold when you open the door), and the fact that the water means less air (which is lost when you open the door) is in the fridge, is why this works at all.

This might be a very good idea, if you have extra space in your refrigerator. I also wonder if you could get the same effect by keeping an empty piece of tupperware in the fridge instead. You would still lose less cold air when the door was opened, and it would take less energy initially.
Of course, if you have a fridge (particularly an old, inefficient one) that is too large for your food (and you aren't planning on adding new people to your household who will be using the fridge), the best thing to do might be to just get a smaller fridge.

Anthony, interesting theory. While I partially agree, tap water is generally quite a bit cooler than room temp. Not always the case, but most of the time. If your tap water is quite cold, there is very little initial cooling to be done.

Another approach is to stop the cold air leaving the fridge, this can be done by filling the fridge with empty containers, anything from tupperware to shoe boxes or even scrumpled up newspaper. This holds in the cold air thereby stopping it needing to be cooled. It also does not require initial cooling.

My fridge is usually pretty bare, and I'm stuck with the one I was supplied with in the apartment. I never thought about it, but I've kept about 6 gallon jugs of refrigerated tap-water in there since about the time I moved in (consider it emergency supplies, perhaps?). I recycle the bottled water as I drink it (trying to ween myself from soda and other "bad-for-you" drinks), but if it's helping keep my fridge from running, awesome!

Also, take things like milk out last and put in first.
Take things you'll cook out first and put away last.
Take everything out at once and put it beside the fridge; then put it on the table or whatever.
The same goes for putting things away: put it all beside the fridge first..
And yes, keep it full, even with empty containers. Replace the bulb with a CF bulb too. It's twice as important here because the heat the bulb produces has to be combatted by the fridge. Although, the fridge light isn't on for very long.

Also, take things like milk out last and put in first.
Take things you'll cook out first and put away last.
Take everything out at once and put it beside the fridge; then put it on the table or whatever.
The same goes for putting things away: put it all beside the fridge first..
And yes, keep it full, even with empty containers. Replace the bulb with a CF bulb too. It's twice as important here because the heat the bulb produces has to be combatted by the fridge. Although, the fridge light isn't on for very long.

Here in Japan, I had an apartment that had the smallest fridge I had ever seen- big enough for one bowl, a bottle, and maybe one condiment. it is awesome! People here generally have no complaints about storing things on the balcony in cold weather, and way small fridges, especially for apartments with one person, are the norm. Love it!

How about the biggest problem with refrigerators, world wide: dirty clogged up cooling coils.

How many of you pull your fridge out, remove the rear cover if there is one, or remove the lower cowling, get a long skinny attachment for your vacuum cleaner, and suck out all the hair/dust debris from the coils, fan blades, and surrounding area?

I'm going to guess maybe 5% of people do this at all, let alone twice a year (or more if you have pets).

Would it be so hard for fridge manufacturers to design the air flow such that it is contained and controlled in a duct, which allows for an easily accessed filter screen? My overclocked gaming PCs have had this for 10 years in order to keep the CPU cool and happy.

Back in the 1950s when my mother was teaching me to keep house, this is one of the things she taught me. At the time, her fridge had a removable grill on the front, so vacuuming was easy and we did it once a month. In order to clean the fridge I have now, my husband has to remove the back panel AND THE INSULATION! in order for me to get at the coils. Needless to say it doesn't get cleaned very often. It's a feature I'll be looking at when we replace our current app.

Another trick my mom taught me is to dust the light bulbs when I clean. You get more light out of them that way and they last longer. Every little bit helps!