First, Ugg Boots are made from sheepskin suede. Like all suede, it is susceptible to water stains. Water spots will leave behind a very slight discolouration when they dry-slight, but noticeable compared to the undamaged suede around it.
To avoid water stains, simply avoid water. Don't wear your UGG Classic Short in the rain, or in marshy conditions. If you wear them in snow, brush the all snow off before going inside.
