Hydrophobes appear in The Colour of Magic. They are magically talented individuals who have an extreme phobia or hatred for water. They are raised as powerful wizards, and from birth they are raised on dehydrated water from the Great Nef desert. Their fear of water becomes so powerful it forms a repulsion field around the hydrophobe that allows them to repulse any nearby fluid. This can be used as a method of transport over water as a group of these wizards can keep quite a large item floating above a body of liquid with ease. All die young as they can not cope with the loathing they feel for their own body fluids.
Annotation, or at least an interesting piece of trivia
In Fortean Times no 315 (June 2014), it is revealed that there is a very rare allergy known as aquagenic pruritus, so rare that there are only 35 known sufferers in the world. Any contact with liquid water causes rashes, swelling, itches, and an anaphylactic reaction if pure liquid water is drunk. (The featured sufferer, oddly, can take tea, fruit juice and soft drinks without the inside of her throat swelling up.) Sufferers are also allergic to contact with their own tears, sweat, or other water-based secretions. Obviously they cannot go out in the rain or travel by boat. There is no known cure. AgProv (talk) 14:00, 3 June 2014 (UTC)