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Drinking Water Quality


Drinking Water Quality Safety and Public Health Risk Dr. Steve E. Hrudey, FRSC, FSRA, PEng Professor Emeritus University of Alberta A National Collaboration on ... – PowerPoint PPT presentation

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Title: Drinking Water Quality

Drinking Water Quality Safety and Public Health
  • Dr. Steve E. Hrudey, FRSC, FSRA, PEngProfessor
  • University of Alberta

A National Collaboration on Risk
  • The Municipal Water Management Research
    Consortium was created by the
  • Canadian Water Network,
  • Alberta Water Research Institute
  • Ontario Centres of Excellence
  • Municipal water leaders posed the question How
    best can drinking water providers address risk
    and uncertainty to assure safe drinking water?

A National Collaboration on Risk
  • International Expert Panel
  • John Fawell, U.K.
  • William Leiss, Canada
  • Joan Rose, U.S.A.
  • Martha Sinclair, Australia
  • Chair, Steve Hrudey, Canada
  • User Advisory Panel
  • Ted Gillespie, Camrose
  • Ian Douglas, Ottawa
  • John Cooper, Canada
  • Donald Reid, Alberta

What Are the Problems with Risk?
  • An unmanageable number of potential drinking
    water contaminants with the list growing
  • Detection limits are improving so contaminants
    will be detected in future where they were not
    detected in the past
  • Public expectations for safe water are not well
    defined, but are certain to be undermined by
    exotic chemical detection without context
  • Lack of understanding by media, and even some
    relevant professionals about the relative
    significance of newly detected contaminants

An Illustration of the Problem
  • e.g. Suzuki Foundation (2006) the water we
  • Recommendation 1 the GCDWQ should be replaced
    with binding national standards that are equal
    to or better than the highest standards provided
    in any other industrialized nation.

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An Illustration of the Problem
  • Many of the lower numbers were based on detection
    limits as a futile surrogate for zero rather than
    on health risk assessment
  • e.g. for 2,4-D, Australia, EU was based on a
    detection limit of 0.0001 mg/L
  • at 0.0000999 mg/L 2,4-D would be reported as
  • that non-detectable but non-zero value could
    still correspond to at least 2,721,260,000,000
    molecules of 2,4-D per litre of water
  • as detection limits continue to decrease,
    drinking water limits could be lowered more than
    another trillion-fold according to this logic

An Illustration of the Problem
  • Simply adding contaminants to a monitoring list
    only adds cost but does little to assure safety
  • WHO Water Safety Plan and Australian Risk
    Management approach correctly focus on
    performance of water safety barriers
  • Focus only on monitoring treated water for MACs
    distracts from focus on barrier performance and
    is unmanageable for small and medium operators
  • Even if resources were not an issue, there is an
    inescapable reality that monitoring for rare
    hazards encounters diminishing returns
    Hrudey Leiss (2003), Hrudey Rizak (2004),
    Rizak Hrudey (2006)

Industry Academic Survey (Rizak Hrudey 2006
Env.Sci.Technol. 405244-5250)
  • Explored the degree of understanding of the
    quantitative interpretation of monitoring
    evidence with 2 professional surveys
  • Australian Water Association members -
    Operators, Public health, Water supply, Water
    management, law and policy
  • 352 respondents
  • 63 gt 10 years experience (38.1 gt20 years)
  • 42 directly involved with interpreting/decision-m
  • Association of Environmental Engineering
    Science Professors, i.e. the teachers

Monitoring evidence for a city has indicated that
in treated drinking water, a pesticide, say
atrazine, is truly present above the recognised
standard methods detection limit once in a 1000
water samples from consumers taps.The
analytical test for the pesticide has the
following characteristics95 of tests will be
positive for detection when the contaminant is
truly present, 98 of tests will be negative
for detection when the contaminant is truly not
present above the detection limit.
Hypothetical Monitoring Scenario to Evaluate Use
of Evidence
With these characteristics, given a positive
result (detection) on the analytical test for the
pesticide in the drinking water system, how
likely do you think this positive result is true?
Provide your scale of agreement below ? almost
certain (95 to 100) ? highly unlikely (5 to
20)? highly likely (80 to 95) ? extremely
unlikely (0 to 5)? more likely than not (50 to
80 ) ? Dont know? less likely than not (20 to
  • 4.54 or Extremely unlikely (0 to 5)

An American academic commented that past
evidence or best intelligence play no direct
role as the law specifies that actual monitoring
data at each sampling point should be used All
that mattered to him was whether you are above or
below the regulatory limit according to
analytical results.
Meaning for Risk Management
  • For detecting hazards we need to know
  • the Positive Predictive Value, PPV
  • PPV is
  • given that you get a positive, how likely is it
    truly present?
  • NOT the Diagnostic Sensitivity
  • given the true presence, how likely will it test
  • to understand what is our ability to avoid false
    positive errors
  • PPV is strongly a function of the frequency of
    the danger that we are looking for

a false positive rate ß false negative
Implications Water Quality Monitoring
  • Medical diagnostic screening programs e.g. breast
    cancer screening (Meyer et al. 1990. JAMA 263
  • for women lt 50 yr PPV ? 8.8 (11 false
    positives per true positive)
  • for women gt 50 yr PPV ? 32 (2 false positives
    per true positive)
  • Hypothetical water quality example for Giardia
    cysts assuming
  • Diagnostic Sensitivity 80, Diag. Specificity
  • Raw polluted water (est. cyst prev. 63) PPV
  • Raw water protected (est. cyst prev. 16) PPV
  • Treated water (est. cyst prev. 1)
    PPV 7.5

Rizak, S. S.E. Hrudey. 2007. Strategic Water
Quality Monitoring for Drinking Water Safety.
Research Report No 37. CRC for Water Quality and
Treatment. Australia. www.waterquality.crc.org.au/
Improving Information Value
  • Make full use of context (supporting evidence)
  • Use sequential confirmatory testing
  • Airport screening (check the positives)
  • Drug testing at Olympics (analyze a split sample)
  • Use parallel testing
  • Use targeted or strategic testing
  • Higher contamination locations
  • Event monitoring with higher hazard frequency
  • Ultimately, the monitoring must be used in a
    meaningful context, NOT as a misleading
    compliance exercise

What is Safe Drinking Water?
  • No current legislation in Canada, including the
    Ontario Safe Drinking Water Act or the U.S. Safe
    Drinking Water Act define safe drinking water.
  • The World Health Organization (2004) Drinking
    Water Guidelines state
  • Safe drinking-water, as defined by the
    Guidelines, does not represent any significant
    risk to health over a lifetime of consumption,
    including different sensitivities that may occur
    between life stages.

What is Safe Drinking Water?
  • Walkerton Inquiry Report - A Strategy for Safe
    Drinking Water (OConnor 2002, p.75) The goal
    of any drinking water system should be to deliver
    water with a level of risk that is so negligible
    that a reasonable and informed person would feel
    safe drinking it.
  • Bonn Charter (IWA 2004) commits to provide Good
    safe drinking water that has the trust of

What is Risk?
  • To understand negligible risk, must understand
  • Risk is a multidimensional prediction of what can
    go wrong consisting of the following elements
  • Hazard the potential to cause harm
  • Probability the likelihood that specified harm
    will occur for a specified scenario
  • Consequences the nature of harm that occurs
  • Time-frame the duration over which the risk is
  • Personal perspectives of those affected about
    what is important to them

What is Safe Drinking Water?
  • Safe drinking water means something like
  • water of such consistent quality, posing no
    significant health risk, that a reasonable,
    accurately informed consumer need have no health
    concerns sufficient to justify seeking
  • A formal working definition is still under
    discussion, but safe inevitably includes some
    aspect of consumer judgement confidence

What is Being Developed?
  • A risk hierarchy based on evidence for drinking
    water including uncertainty
  • Illustrations of how to use the hierarchy
  • Explanation of how risk assessment has been used
    to develop DW guideline MAC numbers
  • A tool kit for informing consumers
  • Examples of using a Water Safety Plan approach to
    assuring safe drinking water
  • Rationale for strategic water quality monitoring
  • Quality assurance advice for water quality data

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