I would like to echo what aimless said.

First you should understand that water treatment is a personal choice and should be based on evaluating the water source you want to treat. My answer may not be the right answer for you. In that vein you need to try to determine what you are trying to protect yourself from/remove: cysts, bacteria, viruses, chemicals, radiation contamination, silt, smells?

Not much you can do about chemicals/radiation contaminants (sometimes can be a problem in the back country due to long gone mining activities). Silt usually requires pre-filtering (through a bandana). If you don't get rid of it, it can clog filters and reduce the effectivity of chemicals and UV treatments. Smells can be improved with active carbon filtering (think Brita but hopefully smaller). Most people say viruses tend not to be a problem in the backcountry in the US (filters usually won't get rid of them, UV and chemical will).

That leaves cysts and bacteria as the main concern to most people. Most techniques are pretty effective at getting rid of the stuff. I have a steripen. It is light (and it doesn't weigh much either) and fast. Some of the earlier models were a bit quirky but they have improved. If you choose this method, you should try it out before you get into the backcountry.

Many people express concern about relying on electronics for water sterilization. They did a study on hikers coming off the AT and found no correlation between water treatment techniques (including no treatment) and stomach problems. They found a good correlation between cleanliness techniques and stomach problems. In other words most people who say they got sick from backcountry water actually got sick from self contamination. I still treat water because the steripen is light and easy, but I don't get overly worried about backup techniques.

You asked about treating water for rehydrating food. If you bring it to a boil, you have treated it. I don't do anything else for water I am going to boil.