We have carpet over concrete and rainy season (and a few
   overflowed tubs and one ... Backed of septic system ... I've
   seen said issue. Indeed it is mystifying. I have a possible
   answer that comes with corresponding emotion of true/this is
   fact. Ignore carpet. You have water on the concrete. Huge
   puddles. Carpet only shows initial boot print at first but the
   puddle of water was already present in other nearby areas under
   the carpet - only revealed later. Fibers in carpet and towel
   alike hold surprisingly less water than a concrete floor can.
   Corn starch holds more, but may be too messy for cleanup.
   Unfinished concrete is also an excellent sponge with many tiny
   hiding holes for water. Porous. Caves. Carpet has caves too but
   not as many. Also if you have carpet padding underneath...
   That's a SPONGE of HUGE surface area. Yet ... I believe most of
   the water was on the concrete itself. Passed through quickly but
   was slower on it's return back up to the surface where you can
   see it and a towel could pick perhaps a 1/2 cup of water at a
   time off of. I measured a few years ago. (Found flax seed a
   perfect temporary damn maker for broken AC drip tray - glutinous
   but amazing. I experimented with many things to soak up/ contain
   water.. Many surprises. Corn starch also a winner. Messy too.
   But this was on concrete/painted latex. Different scenario
   altogether. Water on a balloon vs water on a really hard sponge.
   (Unfin conc). Thus ends brain dump. Thoughts welcomed. Humans
   are lucky with our silicon skin producing silicon oils. Makes us
   nice and waterproof. Poor concrete gets soaked. Even latex
   (rubber/paint/a balloon stretched over surfaces) isn't as good
   as our silicon skin. That's why we wash up so easily. Paint
   doesn't stick to silicon caulking but it does to concrete, which
   is fluffy. Interesting to note: Portland cement is made by
   hydration. It hardens when wet.
   http://www.cement.org/cement-concrete-basics/working-with-concrete/curing
   here is. Cement must stay wet to cure. I wonder if it is ever
   cured of it's thirst of water.