Hey everyone, I stepped on the scale this morning and I was up 4 pounds in one day! I usually obsess over the scale, and this would normally have me down on myself. Here’s the thing, I fasted yesterday, and all I had all day was water. This was a real eye opener for me. I know people are always saying “water can make your weight fluctuate”, but I never really internalized this until today. So, if you step on the scale and you are up a couple of pounds, don’t panic! Turns out all those people who say weight loss is not linear are correct! One other thing that has really helped me is the app Happy Scale. It takes all those little ups and downs and plots them in a way that when you look at it, you see the overall downward trend. It’s very reassuring! Thanks for reading!
I gained 4 pounds in 24 hours! And it's OK!
One other fun experiment (if you have a good enough scale) is to weigh myself before and after my first urination of the morning. The biggest change I’ve seen doing that was 1.6 lbs.
Water is approximately 8 lbs per gallon IIRC.
Or right before bed and right after waking up. I’m usually 3-4lb less in the morning…it’s going out as either sweat or CO2 (or even possibly methane) or a combination thereof, not entirely sure.
In the UK it’s 10lbs per gallon. 
(not everything in the USA is bigger … 
).
https://www.quora.com/How-much-does-a-gallon-of-fresh-water-weigh
I think I’ve seen about 2lb changes…in both directions…so I learn not to get too depressed … or too overjoyed, either.
Saline water has a higher specific gravity than pure water (pure water has s.g. 1 gram per mL). So, expect saline water (i.e. Water with something dissolved in it, like salt) to be heavier in one gallon, than a gallon of pure water without any salt.