When I was blue lighted to hospital with renal colic, I was told that 2 - 3 litres a day was recommended in the summer.
Trying to drink that much is quite difficult. If you gulp water down from a bottle, you'll just pee it out an hour later.
I've recently switched to a bottle with a straw and now drink more, but pee less. The restriction of the straw forces you to slow your intake, but the ease of a flip up straw makes it easier.
Little and often.