Brake fluid is hygroscopic because the interior surfaces of the brake hydraulics are suseptable to oxidation if they are exposed to water. However, brake fluid will hold only a limited amount of moisture. When it saturates, water precipitates out and attacks caliper bores, etc.

Then there is the bigger problem of droplets of water that have precipitated out and are sitting on the bottom of a caliper getting hot and turning to steam, expanding and locking the brake as you drive down a mountain. Not good.

If you live in Tucson, this is probably not a big deal, but if you live where it is humid, changing brake fluid every couple of years is highly recomended.

Brick drivers are a vanishing species....we don't want to loose any!