I think you really have to go at it for drinking water to kill you. Spread over the course of a day, excess water is passed harmlessly. This has led to some faddish diets which advise drinking large amounts when it's not necessary.

I personally drink about a litre a day, none of which is "pure" water but is in the form of coffee, milk etc. I get more water from food and use it in cooking etc - eg rice takes me 300ml to cook of which about 200ml gets inside me. I reckon I could survive indefinitely on 1.5l/day. This is in the UK midlands, with a sedentary, mostly indoor lifestyle.