"drink more water"
lets clarify. this does not mean have more then 2litres.
this means if you regularly drink 2litres of soda.. stop..
change it to 1.5litres of water 0.25ml of fruit juice and 0.25litres of milk
soda when digesting is not treated as water. its treated as a sugar. so your body wont process it and excrete it as urine well. it sits in your body for longer. meaning the 2litre of fluid is 2kg of weight sitting in your body. and you have to work it off more so than water. yes you need to burn calories to get your body to process soda
fruit juice is better because although its treated like a sugar(fructose). it contains lots of nutrients which can be processed by your body. so the calorie burn to burn off 250ml of fruitjuice is less burn off requirement of the same volume of soda
milk is treated like a sugar too(lactose) but also has other nutrients aswell. calcium for one.
but water. well thats needed by your body for many things. every cell needs it. its also needed to burn off calories. so have it in the ratio of 6:1:1 water:fruitjuice:milk
your body only urinates at about 0.5litre per full bladder. so if your only urinating 1-3 times a day. or your urination is not a full steady stream worthy of a full bladder. then you are obviously holding onto more fluid then you should. and so your weight gain or lack of weight loss may be due to consuming too much or the wrong type of fluid