Water can move across the (Semipermeable non polar lipid) membrane by simple diffusion (osmosis).

But polar molecules cannot pass through the non polar lipid bilayer, they require carrier proteins to facilitate their movement.

But water as well, is a polar molecule. How and why does it simply pass through the non polar lipid bilayer by simple diffusion and not by facilitated diffusion (i.e., through carrier proteins)?

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    $\begingroup$ There is a water channel, and a Nobel prize has been awarded for its discovery. To quote wikipedia "Aquaporins are water-channel proteins that move water molecules through the cell membrane." $\endgroup$ – user1136 Apr 30 '19 at 13:07
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    $\begingroup$ @user1136 If you have an answer it should be posted as an answer rather than as a comment. $\endgroup$ – Bryan Krause Apr 30 '19 at 14:00

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