Water retention is also a warning sign that something's wrong (like a hormone imbalance, one of the biggest causes for water retention) and you should probably take it easy. Fat people retain a lot of water. When people start a high-fat diet the first 5 pounds or so are from all the water loss (or even more).

> It's similar to limiting your how much water you drink

Not at all. In fact when dieting it's good to drink a lot of water, precisely to stop your body from retaining it. Odd, isn't it?

aside from hormone imbalances, why do you care at all about water retention?

Because hormone imbalance is the primary reason for why some people are fat and some aren't, being the reason for why type 2 diabetics can die of hunger while still being overweight.

Do some reading on the subject dude.

You should be able to get a relatively accurate number by always measuring your weight first thing in the morning, before drinking anything. You have to be careful not to get fooled, this is some kind of "best possible scenario" because your body loses a lot of water through perspiration during the night, but it'll give you a somewhat solid baseline.