I’ve been walking in the pool for a few months. The water is 1.05 meters deep, and I am 1.83 meters tall, so the water line is just above my belly button. My weight is 100 kg.
So today I decided to walk laps on the balls of my feet. I did 6 laps, probably 600 meters in length with no trouble at all. Tip-toeing 600 meters on land… I couldn’t do that. The water neutralizes a lot of weight.
How do I figure out how much less? Amputations are out of the question.
Buoyancy is equal to the weight of the water displaced. And the weight of the water displaced is proportional to the volume of water displaced. This can be tricky to measure. The classic Archimedes method is step into a bath and note how much the water rises.
If you want a simple estimate, compute the volume of your legs and torso by assuming they are cylinders.
Eureka!
Er, I mean, good idea. 
Or - Fill a suitable container (oil drum?) with water and put it in another container. When you get in you will overflow the drum. Just weigh the overflow.
You could just use a scale if you have an old mechanical one. Being submerged in water for a minute shouldn’t harm it and it should still measure correctly. Double check that it does not use batteries!
I am sure you could also come up with a way to set the scale on the edge of the pool and push down on it with your hands until it carries all of your weight (minus buoyancy).
A couple more possible methods:
Have someone outside the pool hold a hanging scale, and pull down on it until your foot is off the pool floor.
Mark the water line on your belly (or measure with a ruler how far it is above the belly button). Go home, sit in a bathtub and fill it up to the same level. Mark the water level on the side of the tub. Get out. Then measure how many cups of water it takes to fill up the tub to that level. Convert that volume into weight of water.
You’re mostly water, so since it came up about half way figure about half.
I’d make a line at the water level in the tub, and another when the requisite part of my body was in.
My Wife would kill me. 
You folks are awesome. Sometimes wildly impractical, but awesome.
The bathtub seems like the best way to go, and I can mark it with a grease pencil.
Thanks all!
You’d still need to convert the water level difference to volume, and the easiest way to do that is to measure how much water you need to add to bring it up to the higher level.
I guess you could use some kind of tape (perhaps electrical tape, which is reasonably waterproof) rather than a pen. Though it’s pretty easy to clean off a Sharpie mark - just use rubbing alcohol.
