I went from 175 to 172 in one week my first week of eating healthy. So I lost 3 lbs in one week since it was my first week everyone would say it was "water weight". Now I still weigh 172 3 weeks later so I havent lost any more but I am exactly the same weight now so Im just so confused if that was "water weight" does that mean that I have kept the "water weight" off or does it mean I have lost some fat too?

No, it means, you lost solid weight, in my opinion. Tell everyone else to mind their own business. lol

If it were just water weight then it would have fluctuated between then and now. Claim it!