Discussion on WHO Guidelines on Evaluation of Household Water

Treatment Options

Regu P. Regunathan PhDReguNathan & Associates, Inc.Technical Consultant to WQA

10 Aug 2011

Guidelines released • Released in June 2011 after considerable reviews

and discussions

• Intended Audiences are:• National Certifiers• Regulatory Authorities• Researchers• Manufacturers & Implementers

• Arranged in 3 short Sections and 4 detailed Appendices

Tiered ApproachOne of the most contentious subject by reviewers

Modified from original proposal but still retained the essence of the concept . Interim Target approach has been altered significantly.

Based on WHO’s regularly and extensively used target levels of DALY (Disability Adjusted Life Years)

Quantitative Microbial Risk Assessment (QMRA) was employed to estimate Health based Performance Targets

DALYMeasure to estimate burdens of disease and

injuries

Health effects weighed - 0 (good health) to 1 (death)

Years of life lost due to mortality = YLLYears of life lived with disability = YLDDALY = YLL + YLD

10⁻⁶ DALY/person/year = loss of 365 healthy days/one million/year = 1 excess case of cancer/100000 people drinking water over 70 years

Target Pathogens Selected

Bacteria - Campylobacter jejuni

Virus – Rotavirus

Protozoa - Cryptosporidium

Tiers presented

Highly Protective ----- 10⁻⁶ DALY /person/year

Protective -------------- 10⁻⁴ DALY/person/year

Interim ----------------- Achieves “protective” targets for two classes of pathogens & results in health gains in applications.

Health Based HWT Performance Targets

Target Log reduction

- Bacteria

Log reduction

- Virus

Log Reduction

- Protozoa

Highly

Protective

≥4 ≥5 ≥4

Protective ≥2 ≥3 ≥2

Interim Achieves “protective” targets for two classes of

pathogens & results in health gains

Derivation of Targets using QMRABased on known sets of data and several assumptions

Pathogens selected had been cited in GDWQ of WHO along with being involved in several outbreaks

Pathogen levels in raw water calculated on the basis of adding wastewater to a concentration of 0.01%

Daily water consumption, probability of infection by each pathogen, risk of diarrheal illness, and susceptible population were all assumed for the calculations of the DALY and thus these target levels

Technologies described in Appendices

Chemical Disinfection (chlorine, bromine, iodine, chlorine dioxide, ozone, etc.

Filters of all types (Membrane, ceramic, Granular, etc)

Solar DisinfectionUV Thermal TechnologiesCoagulation, precipitation and settlingCombination of relevant technologies

Protocol DetailsTwo types of test waters similar to EPA protocol

Differentiation of protocols based on technology

Alternate indicator microbes suggested (E. coli, MS2, C. perfringens spores, inert particles, etc.)

But not very detailed directions for carrying out the actual tests with the selected pathogens or suggested alternates

Mostly guidelines for development of national regulations and protocols along with certification approaches

Few thoughts

Potentially Simpler ApproachPresent approach for interim targets appears well thought out and

appropriate compared to earlier 1/1/1 log reductions proposed.

Had to make several assumptions to reach these two tiers and targets. Any different assumptions would have lead to very different results

Could have decided on ONE suggested goal to be reached by different countries.

10⁻⁵ DALY/person/year could have been selected as the only one approach

This approach would have lead to targets of 3/4/3 for bacteria/virus/ protozoa. If one gets 4 logs of virus reduction along with 3 logs of protozoan reduction that technology would have easily also achieved 6 logs or more of bacteria reduction. Same as EPA protocol of 6/4/3!!!