Note that Egypt was a lot wetter when the pyramids were built (circa 2500 BCE). http://www.pbs.org/wgbh/nova/next/ancient/climate-change-may...
>Heck, imagine the PSI of water at the bottom of the pyramid columns when they were reaching a hundred feet high?
A column of water 100 feet high exerts 43 psi at its base.
If the mechanics of using the stonework to hold the water were well worked out I would think clay would work well to seal small cracks (and for the scale we are talking about, the 'plumber' could just crawl on in). Or pitch or other sticky stuff.
The density of water is 1,000 kg/m³.
The density limestone is around 2,500 kg/m³ (it can actually go down to around 2,100 kb/m³).
This means that you'd need to displace more than 2 to 2.5 times the volume of water in order to float a limestone block. Keep in mind that volume goes up (roughly) as a cube of the increase in linear dimension, so the difference won't be quite as dramatic as it first seems, but that's still a lot of flotation required. Certainly much larger than the floats shown in the video.
The animal-skin bladder theory is particularly problematic, because the volumetric efficiency of spheroid animal-skin bladder floats isn't particularly good. Water would fill in the space between bladders, requiring much larger float assemblies than if they were able to construct larger, single-chamber bladders. The video depicts float assemblies that aren't even as large as the blocks they were transporting. I found that rather disappointing for an engineering-driven theory.
Tied together, a 1m³ block of limestone and a volume of 1.5m³ of floats displace 2.5m³ of water. Assuming the mass of the floats themselves isn't much then already that would lift 2.5 tons off from the bottom of the water pool.