I drink at least three litres of fluids a day, as you need to take care of all your bodily functions, not just your colon, so fluids are very important.
I alternate my beverages through the day, water, juice, water with cordial, like lime or blackcurrant (go for the natural ones with no artificial sweetners or colours), and so on that way I don't get sick of one drink.
Avoid cabonated drinks, and I find anything too high in sugar can upset my system. Basically, just keep it simple.
And twice a day, I'll have an electrolite replacement drink, like Gastrolite (you get them from the chemist in little sachets that you add to water)
to make sure I'm not flushing too many good salts out of my body (Salt is vital for healthy cells).