Electrolytes like sodium, potassium and chloride should be part of some of your bloodwork throughout TX. That much water under normal conditions would be harmful, diluting them too much, but the drugs seriously deplete H2O in the cells so you need it all. Do what your body tells you.
At 204, 4 liters is probably about right - maybe even not enough if the soda you're drinking is caffeinated, you drink tea, and you work out or your job involves physical labour. If you don't like Gatorade, you might try the packs of 'Emergen-C' powder. It can be mixed into your other drinks, comes in different flavors, and also has different formulations containing additional supplements (i.e. glucosamine/chondroitin).