How do you know if you retain water?

Is there any test or way of knowing? I think I retain, I drink about
4-5 glasses a day. Is it safe to take a diuretic everyday?

Aha! I get the puffy eyelids and jowly also. I had no idea (nor my eye dr) why my eyelids were puffy. I thought the jowly just came because I ate too much sugar or something bad the night before. Ok, I'm gonna have to drink up! Thanks!

For me it's puffy eyelids. I look in the mirror and I look half asleep. I also get jowely. Sodium intake does it for me, too. And drinking lots of water clears it out within a day.

I wouldn't take a diuretic everyday. What's the point of that?

Ruining your health? Losing meaningless pounds (since it's lost fat that matters)?
That's about the only two uses of diuretics I can think of. These things are as evil as daily laxatives... Anne already doesn't drink that much (she's barely at the 1.5l a day, unless that's VERY large glasses she drinks) and diuretics are likely to push her into dehydratation. That's really something that she should discuss with a *competent* doctor (not one specialized in fad diets) before doing anything that might hurt her.
There are some scales that advertise they can calculate water mass. I would expect them to be as inaccurate as the ones that calculate body fat...