I don't like heat, and I'm not a skinny guy. Two weekends ago, it was 33-35C, and I did 35 miles, roughly the same as your 60km each day (Friday, Sat, Sun). I drank when I was thirsty, and went through over two and a half litres every ride. That was just the monitored amount of bottles I bought and/or started with, like andr0id, I like some alternative refreshments, and generally down another glass of water with every pint of ale while biking.

Limiting water seems silly. I'm actually looking at how to carry more.