Introduction

Humans are interesting life forms.  Did you know we have more bacteria, cell-for-cell, living inside us than total cells in our body?  We might also consider that we, as humans, are a solid.  In fact, we are 80% or more water.  Deprive our body of water and the body can rapidly shut down and quickly perish.  Generally, bottled water is sufficient for a short term emergency, but it's not very practical for long term emergencies.  Storing a gallon per day per person for a three week emergency would be 21 gallons for one person or more than 100 gallons for a family of five.  Sometimes it is more practical to have a method to make raw water drinkable or potable using filtration.

Water filtration

 The purpose of filtering water is to remove impurities that could make someone sick including microorganisms and some pollutants. Microorganisms in water could include: protozoa (which include parasites like Giaridia lamblia and Cryptosporidium), bacteria (E. coli, Vibrio cholerae, Campylobacter, and Salmonella) and viruses (hepatitis A and E, Norwalk virus, rotavirus, poliovirus and echovirus). Microorganisms are filtered from water by size (pore size).  Water pollutants including oils, fuels, herbicides, pesticides, and others are removed from water using activated charcoal.  Water filters can be made to filter microorganisms, filter pollutants, or both.  Check carefully with the manufacturer.

Microbial filtration

 Water filters basically allow water to pass through small holes or pores, while trapping impurities larger than pores.  The pores of a filter must be small enough to prevent passage of any dangerous microorganisms.  Basically, smaller pores make for safer water.  On the other hand, the smaller the pores, the more likely the filter gets clogged by soils.

Microorganism size and filtration (2).  

Types of water filters: The two most important elements when deciding what water filter to buy is the pore size and the durability of the filtering element. There are 3 types of water filter elements, ceramic, glass fiber, and hard-block carbon.

• Ceramic elements: These filters are the most expensive because they have the smallest pore sizes, they are the most durable, and the most maintainable. They do not however remove chemicals, poor tastes, odors, or pollutants unless they are combined with a charcoal filter.
• Glass fiber or compressed surgical paper: These filters are mildly expensive and have medium durability but they are usually not cleanable. They do however have small pore sizes that remove most microorganisms but they do not remove pollutants. These types of filters are good for camping and housing purposes but not good for long term use because they are hard to clean and have build up of mold and mildew.
• Hard-block carbon: These types of filters have the largest pore sizes of the 3 types but it is still effective. These filters are less expensive but are brittle and not cleanable. The advantage of using this type of filter is that it is good at reducing chemical quantities, poor taste, odors and many pollutants. Hard-block carbon filters are usually not used on there own but are generally used as a second filter in home and portable water use.

Pre-filters

When filtering water with soils (sediment) present clogs are frequent.  Flow can be improved in a clogged filter by back-flushing or cleaning the surface of a ceramic filter to remove the sediment or soils (4).  Alternatively purchase a filter that provides a pre-filter.  A pre-filter is designed to catch larger soils and remove them before they can clog the main filter.  Pre-filters are easier to clean.

References

References.

1.            Centers for Disease Control and Prevention. A Guide to Drinking Water Treatment and Sanitation for Backcountry and Travel Use. Drinking Water. Available online at http://www.cdc.gov/healthywater/drinking/travel/backcountry_water_treatment.html

2.            Backer HD. Water Disinfection for Travelers. The Pre-Travel Consultation: Counseling and Advice for Travelers. 2011. Available online at: http://wwwnc.cdc.gov/travel/yellowbook/2012/chapter-2-the-pre-travel-consultation/water-disinfection-for-travelers.htm

3.            Dvorak BI, Skipton SO, Dorn TW. Drinking Water Treatment: Emergency Procedures. Neb Guide. 2009. University of Nebraska- Lincoln Extension, Institute of Agriculture and Natural Resources. 

4.            Backer H. Water Disinfection for International and Wilderness Travelers. Travel Medicine. 2002:34; 355-364.

5.            Backer HD. Water Disinfection for Travelers. International Travel. 2010. Available online at: http://www.med.umich.edu/intmed/infectious/travelclinic/documents/downloads/water_disinfection.pdf

6.            Centers for Disease Control and Prevention. A Guide to Drinking Water Treatment Technologies for Household Use. Drinking Water. Available online at: http://www.cdc.gov/healthywater/drinking/travel/household_water_treatment.html

7.            Centers for Disease Control and Prevention. A Guide to Water Filters. Parasites-Cryptosporidium. 2010. Available online at: http://www.cdc.gov/parasites/crypto/gen_info/filters.html

8.            Curtis R. OA Guide to Water Purification. The Backpacker’s Field Manual. Random House March 1998. Available online at: http://www.princeton.edu/~oa/manual/water.shtm