Weightloss question?

Azurastar

Hi Everyone,
I am doing the Cambridge diet . I started the beginning of June lost 12lbs, went on Holiday, gained just 7lb back. I started back on it July7 and have lost 12lbs in the last 6 days. I drink 3 shakes a day, and have a healthy meal for dinner, and I drink a ton of water.
I weight myself everyday, which probably isn't great, but oh well. I weight myself right after using the bath room, I weighed 169. An hour or so later, my son wanted to be weighed to see how "strong" he is getting, and then asked me to do it. I hopped back on was down 1 lbs. I triple checked the scale by weighing a 5lb weight, and weighed myself a couple more times, all with the same 168 reading. Is it possible I lost water weight (that's what I am guessing it was) within an hour?