Hi Fiona and welcome to the HW forum!
My advice would be to listen to your Locum and follow what she suggests, she is there to help you while you are dieting.
As Lady G says, Abbie is doing by post so sure she can help you more with the specifics of doing that way but would agree that water is the key, your Locum will tell you how much to start on depending on how much you drank pre diet (starting on 4 litres a day isn't for everyone if they weren't good with their water to start with)!
Anyway, good luck and you will find that if you follow the diet to the letter, the weight comes tumbling off (did with me, anyway!

) and you'll get those good habits which will hopefully stay with you after you finish.
All the best,
Karen. xx