Water-borne diseases mainly attack people in developing nations, especially where there are few wastewater treatment facilities. Crypto, however, also is a problem in industrialized countries. Chlorine treatments and traditional modern water disinfection practices don't harm the parasite. One of the largest recent outbreaks hit Milwaukee, Wisconsin, in 1993. Some 400,000 people became infected, 4,000 were hospitalized, and 47 died. Nevada, Oregon, and Georgia also had crypto outbreaks. You can learn more about American drinking water from the Environmental Protection Agency.

Where does your drinking water come from? The faucet, right? Actually, that's only the end of a long, complex line. If the source, treatment, and delivery of your drinking water are unsafe, your glass could hold a lot more than you bargained for!

Learn more about water safety in developing countries. Source: CDC: Safe Water System

Scientists estimate that a billion people worldwide lack any access to potable, or drinkable, water. The problem is acute in the developing world, but it's not limited to poor countries. Almost 800 communities in the United States allow sewage and wastewater to run into rivers and lakes during heavy rainfalls. These same rivers and lakes then supply drinking water. You can find out more about the risks to drinking water in the U.S. from the Environmental Protection Agency.

Countless microbes—including bacteria, viruses, and parasites—can lurk in water. Humans cannot see or taste these unwanted ingredients. In fact, people can even get sick from unsafe water without realizing what has happened. Biological contaminants can often produce mild symptoms: diarrhea, nausea, or abdominal cramps. It's easy to blame a spicy meal or other things while the real problem—contaminated water—goes unnoticed and unresolved.

But water supplies can also transmit deadly diseases, such as hepatitis or cholera. These ailments can easily kill those with weakened immune systems. They harm many healthy people too. The World Health Organization estimates that unsafe water takes the lives of four million people—mostly kids—each year.

One disease that illustrates the importance of safe water is cryptosporidiosis ("crypto" for short). Crypto is caused by a microscopic parasite that lives in the intestines of humans and other vertebrates, including cattle and deer. When infected people or animals relieve themselves, their waste includes the parasite. Thanks to a tough outer shell, the crypto parasite can survive for weeks outside of a host body. So the disease spreads fairly easily. Indeed, crypto appears to be on the rise.

The small green circles are crypto parasites. Source: Center for Disease Control and Prevention (CDC)

Outbreaks frequently follow heavy rainstorms. What often happens is that rain falls on hillsides or pastures littered with dung from infected animals. Rainwater then washes the parasite into streams and lakes. The parasite may also come from leaking septic tanks. As a result, people who drink, wash with, or bathe in the water pick up the crypto parasite. Fine filtration is the best way to prevent crypto contamination.

Crypto usually isn't deadly, though it can kill people with weakened immune systems. For the most part, the disease causes diarrhea, abdominal cramps, and fever. These symptoms usually begin a few days after a person becomes infected and linger for about two weeks. Like many diseases, crypto has no cure. Patients must simply wait it out—and take in plenty of fluids to avoid dehydration.

You can find a crypto fact sheet at the Centers for Disease Control website.

Will global warming affect the spread of cryptosporidiosis? Possibly. Environmental changes and shifting weather patterns might make rainstorms more frequent. That would give the durable, dangerous crypto parasite more opportunities to invade our water.

How can you protect yourself from unsafe water?