Even when the water looks completely clear, it may be contaminated. There are two classes of contaminants: chemical and biological.
While all water contains some chemicals, unusual or dangerous chemicals dissolved in the water are chemical contaminants. Some chemicals can make water taste good or add flavor. Sugar and salt are both chemicals that can invisibly change the flavor of water. Other chemicals can make water poisonous to plants and animals.
Biological contaminants are microscopic organisms that can live in water but are usually invisible to the human eye. Biological organisms in water can be beneficial to humans: Nitrosomonas bacteria helps break down ammonia, a chemical contaminant. But when biological organisms are harmful or unusual in water, we say they contaminate the water. Biological contaminants can be deadly: Cryptosporidium parvum and Giardia are both one cell parasitic organisms that cause a waterborne stomach illness that visits cramps, watery diarrhea, and fever on its victims.Water