This 3rd Party Setting uses a chinchilla-based method of water purification

[Libertad]

Sands of Eiklatha is a desert-based campaign setting with several interesting features, from playable undead race to theocratic frogs who view the sands and sun as evil and guard rivers and oases from them.

However, there is one aspect which stands head and shoulders above all others, the Water Chinchilla!

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Water Chinchilla CR 1/3

XP 135
N Tiny animal
Init +2

Defense
AC 14, touch 14, flat-footed 10 (+2 Dex, +2 size)
hp 6 (1d8+2)
Fort +4, Ref -1, Will +0

Offense
Speed 30ft., swim 30ft.
Melee bite -2 (1d3-4)

Statistics
Str 3, Dex 8, Con 14, Int 2, Wis 10, Cha 14
Base Atk +1; CMB +1; CMD 7
Languages None
Ecology
Environment River
Organization solitary, cage (3-7), barrel (8-20)
Treasure none
Special Abilities

Purify Water (Su) A water chinchilla placed in any liquid will absorb up to two gallons of the liquid into their body. Once at least one gallon is absorbed in this way the water chinchilla will loose it's land speed but gain +2 natural armor due to swelling. If squeezed, any liquid inside the water chinchilla will be wringed-out, this does not harm the water chinchilla. Liquid that has passed in and out of a water chinchilla in this manner is treated as if it has had the Purify Food and Drink spell cast on it with a caster level equal to the water chinchilla's hit dice. A water chinchilla may only purify 2 gallons of liquid per day in this manner. A water chinchilla that absorbs a liquid is subject to the same negative effects that would be inflicted upon it if it drank that liquid, though it gains a +2 bonus to Fortitude saves against the effects of those liquids.

Water chinchillas are small, almost spherical creatures with gray fur. They have large rabbit like ears. When a water chinchilla touches water they absorb it and swell up like a balloon allowing them to swim around easily.

This cute, adorable animal is a highly prized creature for its ability to turn brackish water into clean drinking source. They are commonly sold along the banks of river villages and in adventurer's shops, on their own or in water-filled barrels of 10.

And yes, they can be obtained as familiars.

Even the most jaded of gamers will grow to love these fuzzy little rodents if not for their adorableness, but for their vital function in an arid desert-based campaign. Just picture it; chefs at restaurants holding the bloated furry creatures over plates, squeezing out soups and drinks for thirsty patrons! A sudden rainstorm causes the sorcerer's familiar to balloon up in reaction. This is the perfect way to inject some lightheartedness into a harsh desert setting, and I might just borrow this creature for my home games.