Cysts are the one celled, egg-like forms of some protozoans. Some are found in water and while a number are harmless, others such as Giardia and Cryptosporidium cysts can lead to disease. It's difficult to kill these cysts because they're protected by a tough outer membrane that resists even chlorine bleach.

People ingest cysts by drinking contaminated water, which are deposited in lakes, rivers and streams through human and animal waste. The Cryptosporidium cyst leads to a disease called cryptosporidiosis, which symptoms start between two and 10 days after the person has ingested the cysts. The main symptom is a watery diarrhea that's accompanied by cramps, fever, nausea, vomiting and weight loss. The diarrhea and vomiting can become sufficient enough to leave the person dehydrated. Giardiasis has similar symptoms and can affect the person for years.

Giardiasis and cryptosporidiosis are dangerous for people who have a weakened immune system, although healthy people usually recover from the maladies. Still, it's not unusual for patients with Giardiasis or cryptosporidiosis to relapse before the disease goes away completely.

Water Filters and Cysts

Although shocking water with chlorine does not destroy the Giardia and Cryptosporidium cysts, they can still be kept out of drinking water. One way is through a water filtration system based on activated carbon or charcoal. Cysts are quite large when compared to the pores in these filters, and about 99 percent of them can be prevented from entering the drinking water. Users should look for systems that have an absolute pore size of 1 micron or lower.

The good news about activated charcoal filters is that they can be attached to the point of use, such as individual faucets. They are inexpensive and do not need to be installed by a plumber. They are also available as pour-through pitches. The filters need to be replaced now and then, and the job should not be done by someone who has a compromised immune system.

Reverse Osmosis

Another water filtration system that works against both types of cysts is reverse osmosis. Reverse osmosis uses a semi-permeable membrane to block toxins and pathogens but is more complex than an activated carbon system. It is best installed by a plumber either where the water enters the building or at point of use.

A filter system should have a label that tells the buyer that it can remove Giardia or Cryptosporidium specifically or that it has been tested for either cyst removal or cyst reduction. Inferior filters remove Giardia but allow the smaller Cryptosporidium cyst to pass through.

These water filtration systems prove that it is quite possible to prevent disease-causing cysts from entering drinking water. This goes a long way in supporting the health of members of a household.