Drank only 1.5, put on 3.5!

I don't dialyse on Sundays and so have to be extra careful with fluid on Sundays and Mondays till my dialysis session starts on Monday night.

This Sunday, I measured everything I drank and it was 1.5 liters including some fruit I had. But on Monday morning when I checked my weight I was 3.5 kilos over my closing weight of Sunday morning. Now how can you explain that?

Well, food we eat also has water but then we also lose water by perspiring. All told, that shouldn't add so much - 2 liters.

Sometimes I think even when I restrict I am putting on 3.5 kgs and even when I am liberal I put on about the same. So, why bother?