Ah yes...
It was my 'scales are stupid' rant.
Whatever the scales say, so long as you are doing the diet 100%, you will be losing fat. Depending on what you currently weigh, you will be losing between 2 and 4 pounds of fat a week (maybe even slightly more).
Unfortunately, your body doesn't like that you're losing weight so quickly. It makes it upset. In order to control your blood pressure and balance your blood sugar levels and make all your internal organs do their job, it actually likes things to stay the same. It can't do much about the fact that you're losing fat - but it can hang on to more of the water that you're putting into it. In fact, there is a theory that as your fat cells shrink, they initially fill up with water instead - just in case you change your mind about losing weight and it needs to use them in a hurry to store fat. Once your body is convinced that you don't need that fat cells, it'll let the water go, and let the fat cells shrink permanently (woohoo!).
And - you'll have guessed by now - week 3 is a classic time for that water retention thing to happen. It happens to some people in week 4 instead. In fact, the whole way through your weight loss journey, there will be the occasional week where you inexplicably only lose a couple of pounds, a pound - or even... gasp... you don't lose anything at all, despite being 100%.
It's all entirely normal.
It doesn't mean you're not losing fat. It means you're retaining water.
For what it's worth, I don't think you need to drink more water. You could probably do with a more realistic and encouraging CWPC though...
On Cambridge, with four stones to lose, you can expect to lose between 3-4 pounds a week on average. The key thing is that word
average. There will be weeks where you lose 2 pounds and weeks where you lose 5. Next week might well be the week that you lose 5 pounds - if you can stay away from the cooked breakfasts.