Why does drinking alkaline water help my body process chemicals from chemo?

It really doesn't. The idea that alkaline water will help your kidneys excrete chemotherapy is simply not true. Whatever you swallow is exposed to hydrochloric acid (stomach), followed by alkaline enzymes (small intestine). You cannot change the pH of your blood, or increase excretion of chemotherapy, by drinking alkaline water. Drinking lots of any water will help rid your body of chemotherapy!
Yes. Increase urineexcretion.
No. Every chemotherapy is different. There are no set rules.