Can't I drink juice or something instead of plain water?

Yes, you can. Of course you can. This one just baffles me. I've heard nutritional "experts" tell people that they can't "get by" drinking juice, soda, tea, coffee, or milk, or whatever, for their daily intake of water, and no matter how much they drink of these other things, they still need to drink 64 ounces of plain water a day. Do these people even have brains? This is one of the most absurd things I have ever heard. Apparently somewhere in whatever process passes for thought in these people, add a couple percent of something to water that makes it actually taste good, (or even have a taste) and somewhere along the line all the water in it disappears.

What do you suppose most beverages are made of? Even whole milk, as thick as it is, is still about 88% water. Many sodas are around 99% water. Pure juices are usually somewhere in the middle. But, all of them are mostly water, and from them your body gets hydrated.

Of course, the jury is still out regarding beverages with a diuretic effect, but anyone who has drunk more beer in an evening that was probably good for them can attest that one of the things they don't wake up feeling is hydrated. So, one must use common sense, and listen to their body. However, it should be mentioned that in the days before sanitation, often beverages containing alcohol were far safer to drink than water. Beer and wine were often consumed in much higher quantities than water. On long voyages, for example, beer was often the only beverage the crew was served, along with the occasional tot of rum. You see, nasty critters that cause nasty things like dysentery don't grow in an environment that contains alcohol, but they often grow quite happily in barrels that contain plain water. So, beer was the beverage to take on long sea voyages. Apparently the folks on those voyages didn't die of dehydration, though it is probable that the alcohol content of that beer was much lower than modern varieties. Or, of course, this could be where the whole "Here be Monsters" thing came from. :)

Coffee is another, for me, at least, that I don't drink if my aim is to become hydrated.

Am I saying you should substitute other beverages for water? Well, not necessarily. Most sodas, and even fruit drinks and juices, for instance, have a ton of sugar in them. Sugar is not a necessary nutrient, and is not good for you, no matter its origin. Your body makes fat by storing the excess energy of the glucose in your blood that you do not burn immediately, and sugars of all sorts are the most easily and quickly turned into glucose in your bloodstream. Glucose, of course, is only a very pure form of sugar, and this, along with oxygen, is what your body runs on. But, glucose is what the digestive system eventually turns most everything you eat into.

The problem occurs when you dump a bunch of stuff in your stomach that turns almost instantly into glucose in the blood. Too much glucose, and your body makes insulin to get it out of your blood. But, excess glucose doesn't simply vanish, as most people seem to think. Your body is much too frugal for that. It converts the excess energy to fat, to be used as a food source in times of famine, or at least actual hunger.

But this is (and will be) a topic for another post. For now, let's just say that constantly substituting sugary or diuretic drinks for water is probably not a good idea. But aside from those two caveats, drink whatever you like, and your body will still get the water it needs. Oh, and unless you are doing something really taxing, like running a marathon, or cutting wood for hours at a time, energy drinks are evil. All they are is a combination of all the stuff that makes your body hyper, in huge quantities. Aside from the crash you get later, they're just plain bad for you. At the very least, they'll make you fat.