I'd add that diet can make a big difference too. Junk fast food and ready-meals can have bad stuff in it, but so can posh restaurant food. The restaurant people mainly care about it tasting good so they put in loads of fat and salt. If you prepare your own food from fresh ingredients you know what you are getting.

For example, last night I had a microwave pizza, and I also had a litre of pineapple juice with it. That meal caused me to roughly double my fluid intake for the day, to deal with it. I drink more after Chinese food, too. If you habitually eat out or eat ready-meals, that can contribute to your needing to drink a lot.