If your intake was only water then yes you would lose weight but you would do untold internal damage, some life threatening. So I doubt you mean that.
For healthy skin and body you need to consume around 2 litres of water a day, this would increase if you are very active or in a very hot area.
The way to lose weight is to cut down on your calorie intake but making sure you have a selection of food from all groups (fruit, veg, carbs, meat/fish, dairy, sugar/fat) otherwise you not only risk not getting the nutrients and vitamins you need but when you reintroduce that food you will probably gain the weight you lost and more. If you were to drink a glass of water before a meal then this would fill you up slightly so you could eat a smaller portion.
The other thing that works along side a sensible diet is exercise. This can just include a brisk 30 minute walk if the gym isn't for you.