Homewrap is not waterproof - just extremely hydrophobic. You cannot make a water bag out of it: the hydrolic head exceeds its capacity. On the other hand, if you make a tarp out of it and set it up in the rain next to a normal silnylon tarp, the silnylon will have mist-through, but the Tyvek will not. its pores are not continuous -as are the pores in silnylon. When a raindrop hits a silnylon pore some water will squirt through. That does not happen with Tyvek.

On the other hand, the pores of silnylon are quite small, so sylnylon will hold a higher head of water than Tyvek. All that means in practice is, make water bags and ground sheets out of sinylon and tarps out of Tyvek, not the other way around.

The misting phenominon is complicated. It has been confused with condensate being knocked off the tarp. In fact, that does happen. But there is also bono fide splatter through that happens on a tarp that is bone dry on the under side. It is not intuitively apparent because it would seem inconsistent with the fact that silnylon will hold a few inches of head without weeping. The answer lies in the instantaneous pressure that portions of a rain drop can exert. That pressure can easily exceed the resistance of the microscopic pores in silnylon. Sn doesn't leak easily because of a combination of the hydrophobic polarization of silicone and the surface tension of water. A fast moving rain drop will sometimes generate enough pressure to overcome both sources of resistance.