I'm currently training for a marathon (my first, so I am new to this) and here is what I have found regarding water...
My dehydration level during running has a LOT to do with what I drink the day before. It is highly stressed in my training class to drink adequate amounts of water on Saturday before our early morning runs on Sunday. This way your body is fully hydrated BEFORE you go out for your walk/run.....and go to the bathroom right before you head out, even if you don't feel the need (empty out the bladder)
There are about 100 people in my training class and their water habits vary. Some people freeze one bottle and leave one unfrozen. This way, after they finish the first bottle, the frozen one is defrosted and cold to drink. Some people put sports drink in one of their bottles and water in the other. If you don't like the sports drinks because they are too sweet, try watering it down or getting the low cal/light varieties. I find these aren't as sweet and overpowering. For 8 miles, if you are properly hydrated and fueled before you head out, you probably don't NEED to have extra sodium on your walk....but that is just my opinion. If you can find a variety you like, drink a little before you head out and a little when you get back. I don't think they are necessary, but they can be helpful.
I used to get sausage fingers all the time when running. I have found that as I improved my diet and started eating more fresh fruits and veggies and cutting processed and fatty foods it has completely stopped. When it is really hot (or if I had a night out drinking the day before
) I found that the swollen fingers return. I am not positive about the cause, but mine seems to be related to TOO MUCH sodium and not enough water. If my fingers start to swell, I need to drink more... not add salt. It was also a circulation problem with me. I have poor circulation in my hands and started taking some vitamins for it and that has helped too.
Hope this helps and keep up the good work!