I just got a scale and started weighing myself once a week. How can you tell the difference between water weight and fat?

the weight you lose right at first will be water weight...after that you 'll lose fat.

yes and no- you do lose water weight first, but it's not always fat that you lose after... if you're working out too hard, you're burning muscle before you get a chance to make it... Make sure you're in your optimal heart rate and you'll see results.

stick with it!!

not in your optimal heart ratel to burn fat you should work between 50 and 70% of you max heart rate. 70-85% of you max heart rate will cause and incread in your cardio vascular system (fitness) and over 85% works your anaerobic systems.

to burn fat stick for at least 30 mins at about 60% of your max. (max is 220-your age) so if your 20 your max is 200 60% of which would be 120beats per min.

as for water well without impedance scales its hard to tell but if you cut back on your salt intake and up your water intake you'll drop stored water amounts. in the average 250 person they say upto 15lb can be stored water. unfortunaly women are prone to retain water at various stages of there cycles so if your weighing weekly you'll notice the difference in that.