FILTRATION REGULATIONS AND RECOMMENDATIONS

The Center for Disease Control and the Environmental Protection Agency have established protocols and minimum national standards for filtration and treatment of potable water in a back-country environment.. Other agencies, including the National Park Service, have established rules and recommendations for water purification that are applicable within their jurisdiction. The regulatory agencies guidelines are not all the same. (See the tables below.) The end user should determine which regulations or recommendations apply in their location.

The filters systems we build, when used in conjunction with chlorine treatment, will remove and/or reduce viruses, enteric bacteria (E. coli), Cryptosporidium oocyst and Giardia cyst and produce safe potable water. (Filtration will reduce suspended solids but the filter elements we use are not designed to remove chemicals or dissolved salts.)

FILTER TERMS

Microns – Filters elements are typically rated in microns. A micron is one millionth of a meter.

Absolute vs. Nominal - Most filters elements are labeled either “nominal” or “absolute”. Elements labeled “absolute” are supposed to remove 99.98% of the particles equivalent to the micron rating size at a flow of 10 liters per minute.

A “nominal” rating on a filter element is impossible to quantify. The nominal rating means that the element is supposed to stop some undisclosed percentage of the particles the size of the micron rating. It could be 20% or 80% or any other percentage the manufacturer chooses. A nominal 20 micron element that is 80% efficient can also be marketed as a 1micron nominal element even if it is only 20% efficient at the 1 micron rating. The majority of filter elements, even those that are labeled as “absolute”, are not independently tested.


NSF rating - The National Sanitation Foundation is a non-profit, non-governmental organization that does certify some filter elements. Some of the regulations call for filter elements that are “1 micron absolute or NSF Standard 53 for cyst removal”. Obtaining NSF certification for a filter element is very expensive, so there are only a few manufacturers that make elements that are certified to the NSF standard. The Doulton Rio sterasyl ceramics element we use in the "Grand Canyon" filter is NSF certified.  Ceramics elements will not provide adequate flow for our gravity filter so we recommend 1 micron absolute synthetic elements in that application. (They work well and are much more economical than NSF certified elements.)

Organism	Average Size (µm)	Maximum recommended filter rating (µm Absolute)¹	Filter rating absolute	Filtration effective	Chlorine effective	Filter and Chlorine
Viruses	0.03	Not specified	1.0 µm	-	+++	+++
Enteric bacteria (E. coli)	0.5 × 3.0–8.0	0.2–0.4	1.0 µm	-	+++	+++
Enteric bacteria (E. coli)	0.5 × 3.0–8.0	0.2–0.4	0.3 µm	+++	+++	++++
Cryptosporidium oocyst	4–6	1	1.0 µm	++	+ to ++	++++
Giardia cyst	6.0–10.0 × 8.0–15.0	3.0–5.0	1.0 µm	+++	+++	++++

¹ NSF 53 rating on a filter certifies for cyst/oocyst removal.
Source: http://www.cdc.gov/healthywater/drinking/travel/backcountry_water_treatment.html

 Table Key

-	not effective
+	low effectiveness
++	moderate effectiveness
+++	high effectiveness
++++	very high effectiveness

           Grand Canyon - rules and recommendations for treating water with filter and chlorine

Source for treatment process Alum Chlorination¹ Filter National Park Service - M. Walburger GCRG Guide Training 2009 Treat with Alum if sediment in water  1/4 teas. bleach per 5 gl. add until residual test shows 1 ppm free Cl. ≤ 1.0 micron Grand Canyon National Park Commercial  Requirements 2012 - add 6% chlorine bleach until residual test shows ≥ 1 mg/l free Cl NSF standard # 53 for "Cyst Removal" or 1.0 micron absolute Grand Canyon National Park Noncommercial Regulations 2011 1 teas. per 5 gallons 2 drops chlorine bleach per gallon after filtering filter ≤ 0.2 micron nominal

UV Water Sterilization

The use of ultraviolet light as a viricide and bactericide is becoming more common in the treatment of drinking water. It is of limited use in a backcountry setting for a number of reasons.

“UV light can be used as a pathogen reduction method against microorganisms. The technology requires effective pre-filtering due to its dependence on low water turbidity (cloudiness), the correct power delivery, and correct contact times to achieve maximum pathogen reduction. UV might be an effective method in pathogen reduction in backcountry water. However, there is a lack of independent testing data available on specific systems.” (Center for Disease Control water disinfection yellowbook)

From just a “compliance” standpoint some regulatory agencies specifically state that it is an unacceptable method.

“Any alternative disinfection method must be approved by the Public Health Consultant. Use of ultraviolet light as an alternative to adding disinfectant will not be approved.”  (NPS Grand Canyon Commercial Operating Requirements 2009)

Here are a few more more reasons to avoid UV disinfection:

• When the quartz UV tube gets fouled the UV light does not disinfect the water.
• The quartz tube needs to be inspected and cleaned regularly.
• The quartz glass is fragile.
• There is no external indicator that insures the UV light is working when the system is running.
• The UV light should be illuminated before there is flow through the system.
• Contact time is critical and flow has to be slow enough to make it effective.

Take a look at the EPA publication “Ultraviolet Disinfection Guidance Manual for the Final Long Term 2 Enhanced Surface Water Treatment Rule” (2006) which is available on the Internet. This manual is intended for municipal treatment facilities, but the 436 page “Rule” illustrates the complexity of using UV effectively.