Its a waterborne parasite that is commonly called the Brain eating Amoeba and its biologically given name is "Naegleria Fowleri". It lives in warm, unclean water. It directly effects the nervous system, though it occurs rarely but in case it happens it is difficult enough to treat and leads to death in about a week.
The disease doesn't spreads by drinking water but quite often it spreads by swimming in dirty water or while cleaning up your nostrils with contaminated water. As this dirty water enters your nostrils this Amoeba travels through your nose to brain and starts effecting the nervous system and destroys its delicate tissues. Symptoms include fever, nausea, vomiting, stiff neck and headaches.