That's a good loss for a week, FC. Good on you!
If you do a lot of exercise there's a chance it's increasing your appetite and you might be eating more calories than you are burning. Have you looked at the calorie and fat content of what you're eating? I used to think I was eating a healthy diet until I worked out that my portions were WAY too big and the 'healthy' food I was eating was quite high in fat (and recently - sodium, so I'm now cutting down on salt too).
Personally I think that 400g per week is a good healthy weight loss rate, so I don't think there's any need for major tinkering. Drinking a bit more water is always good, but let your thirst guide you. Don't go force feeding yourself water because there's no benefit in that!
You're doing really well so far, FC.