This article is from the Hiking Boots FAQ, by Chris Gilbert email@example.com with numerous contributions by others.
Some manufacturers these days coat their
boots with a hydrophobic substance which is an effective repellent
for water but which will eventually wear off. The boot should be
periodically cleaned in warm, clean water and allowed to dry
naturally ( as opposed to dry by placing next to a heat source).
Leather boots should *never* be force-dried as it will encourage the
leather to crack) before applying one of a number of different
waterproofing/conditioning substances all of which have their merits
and demerits; Natural Wax (Dubbin) is readily absorbed but may
cause the leather to become overly pliable with prolonged use.
Synthetic Wax (eg. Nikwax) is best applied with the fingers as the
warmth makes it easier to apply. Liquid Repellents ( eg. Liquid
Nikwax ) are applied with a brush and do not have to be 'forced'
into the stitching of the boot. Prolonged application of liquid
reppellent may also cause the leather to become overly pliable. If
your boots get really wet then you should stuff them with newspaper
to draw any water out of the liner while the leather is drying. The
newspaper should be replaced periodically.