Is there a good precedent for the "foul water" ability?
vsA peltast exudes any waste material from itself whenever immersed in water (thus staining and poisoning the water; anyone who drinks the same water must save vs. poison at +2 or become nauseated for 2-8 rounds, unable to attack or defend).
Corrupt Water (Sp): Once per day an adult or older black dragon can stagnate 10 cubic feet of water, making it become still, foul, and unable to support animal life. The ability spoils liquids containing water. Magic items (such as potions) and items in a creature’s possession must succeed on a Will save (DC equal to that of the dragon’s frightful presence) or become fouled. This ability is the equivalent of a 1st-level spell. Its range is equal to that of the dragon’s frightful presence.