I had my period 2x b4. i think is my third. i have drunk a lot of water in the past few days 2l+ and 4 3 days i hav brown discharge whenwillitstart?

It depend on: When your last period was. Not on how much water you drink. You need to count the days between your period to know when to expect the next period will start. That's how you will figure it out!

See below: It may be helpful to keep a calendar and mark the days when you have your period. Usually your 'cycle' is 28days from the first day of bleeding until the next first day. Sometimes keeping track helps. However, when you first start your periods, the cycle may be longer or shorter than 28 days. Don't worry about it, just keep track it should normalize for you.