ISO 9111:2024

International
Standard
ISO 9111
First edition
Water reuse in urban areas —
2024-06
Guidelines for benefit evaluation of
reclaimed water use
Recyclage des eaux dans les zones urbaines — Lignes directrices
concernant l'évaluation des avantages de l'utilisation d'eau
réutilisée
Reference number
© ISO 2024
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 2
5 General . 2
6 Indicators of benefit evaluation of reclaimed water use . 2
6.1 Holistic indicator system .2
6.2 Resource benefits .3
6.2.1 Conventional water resource savings .3
6.2.2 Energy resource recovery .3
6.2.3 Carbon resource recovery .4
6.2.4 Phosphorous resource recovery.4
6.3 Ecological and environmental benefits .5
6.3.1 Reduction of contaminants .5
6.3.2 Reduction of electricity use .5
6.3.3 Reduction of greenhouse gas (GHG) emissions .6
6.3.4 Achievement of E-flows .6
6.3.5 Ecosystem protection/restoration .7
6.4 Social benefits .7
6.4.1 Improvement of local natural environment .7
6.4.2 Improvement of regional natural environment .7
6.5 Economic benefits .7
6.5.1 Avoided cost .7
6.5.2 Net present value (NPV) .8
6.5.3 Internal rate of return (IRR) .8
7 Procedures of benefit evaluation of reclaimed water use . 9
7.1 Benefit evaluation flow chart .9
7.2 Procedures and considerations of benefit evaluation .10
Annex A (informative) Indicators for the evaluation of natural environment improvement by
reclaimed water use in the social benefit category .12
Annex B (informative) Recommended evaluation indicators for different scenarios .13
Bibliography .15

iii
Foreword
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This document was prepared by Technical Committee ISO/TC 282, Water Reuse, Subcommittee SC 2, Water
reuse in urban areas.
Any feedback or questions on this document should be directed to the user’s national standards body. A
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iv
Introduction
Water shortages are recognized to be some of the most crucial threats to sustainable development of society.
Reclaimed water is a safe, reliable and sustainable water source to help satisfy water demands, especially in
many water-scarce areas. Today, reclaimed water is used in urban areas, including agricultural irrigation,
ecological or environmental flow replenishment, landscape irrigation, toilet flushing, firefighting, and car
washing amongst other uses. Implementation of principles of benefit evaluations can create thorough,
comprehensive, systematic, and sustainable reclaimed water use. However, the intrinsic values or the
benefits of reclaimed water use are not clear. There are limited guidelines or regulations currently available,
specifically regarding the benefit evaluation of reclaimed water use in urban areas at a global level.
It is important to establish a systematic, scientific and holistic benefit evaluation system for reclaimed
water use. Based on the different applications of reclaimed water and the varied water quality requirements
linked to the intended use, it is important to evaluate the benefits of various indicators for reclaimed water
use. The benefit evaluation should take into account various indicators such as the resource, ecological and
environmental, social, economic and other benefits, including the reduction of global warming.

v
International Standard ISO 9111:2024(en)
Water reuse in urban areas — Guidelines for benefit
evaluation of reclaimed water use
1 Scope
This document provides guidelines to evaluate the benefits of reclaimed water for applications requiring
different levels of water quality and for beneficial use in urban areas.
This document is applicable, among others, by practitioners and authorities to assist water reuse planning,
design, operation and management.
This document provides evaluation indicators, procedures and examples of reclaimed water use benefits.
Design parameters and regulatory values of different reclaimed water uses as well as risk or safety
evaluation of reclaimed water use are out of scope of this document.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 20670, Water reuse — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 20670 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
benefit evaluation
analysis contributing to decision-making on whether to adopt a project or a plan by quantifying and
comparing its benefits
3.2
ecological or environmental flow
E-flow
water flow and level that allows to sustain aquatic ecosystems which, in turn, support human cultures,
economies, sustainable livelihoods, and well-being
3.3
avoided cost
benefits occurred as a result of avoiding unnecessary costs while meeting demand requirements and
thereby avoiding the additional resources and service waste
Note 1 to entry: This concept is from least cost or integrated resource planning.

4 Abbreviated terms
COD chemical oxygen demand
CO -eq CO equivalent
2 2
GHG greenhouse gas
IRR internal rate of return
LCC life cycle cost
LCY local currency
NCF net cash flow
NPV net present value
P phosphorous
5 General
Ensuring safety of reclaimed water is crucial to protect the environment and human health from the adverse
effects of toxicants and pathogenic microorganisms. Generally, the reclaimed water safety assessment (e.g.
ecological and human health risk assessment) can be conducted before implementing benefit evaluation
of reclaimed water use. For detailed information on risk assessment and management, ISO 20426 and
ISO 20761 can be used as references. Moreover, the supplied reclaimed water quality should also meet the
requirements of local specifications and end user demands.
In principle, benefit is evaluated based on the comparison between the water reuse option and the business-
as-usual or other method using alternative water resources, which are referred to as baseline. The relevant
option and baseline are evaluated under the same conditions with the same indicators. The baseline can
include a do-nothing scenario where no solution other than water reuse can realistically be envisioned and
the baseline is to do nothing. The benefit of water reuse is expressed as the difference between the indicators
for the relevant water reuse option and the baseline.
The benefit evaluation of reclaimed water use should comprehensively consider resource, ecological and
environmental, social and economic benefit aspects.
The benefit evaluation of reclaimed water use includes quantitative and qualitative analyses, with
corresponding indicators. The indicators should be set specifically, objectively and easily for calculation
and/or comparison.
Wastewater treatment plants can be included in the boundary if necessary, as is often the case in
comprehensive evaluations. The baseline scenario and the evaluation boundary including conventional
wastewater treatment processes should also be determined for the benefit evaluation which is based on
comparisons with the water reuse scenario.
Different water reuse projects and different utilization scenarios can be evaluated separately. Afterwards,
the overall evaluation or comprehensive evaluation results can be obtained.
6 Indicators of benefit evaluation of reclaimed water use
6.1 Holistic indicator system
The indicators for benefit evaluation of reclaimed water use can be classified in four categories: resource,
ecological and environmental, social and economic.

The main indicators for different benefit evaluation categories are listed in Table 1. If necessary, other
indicators can be considered and incorporated for evaluation. Annex A provides examples of indicators for
the evaluation of natural environment improvement by reclaimed water use in the social benefit category.
Evaluation indicators can be selected according to the evaluation needs and reclaimed water use
characteristics. A comprehensive evaluation system should contain a reasonable number of indicators in
terms of different aspects and avoid repetition.
Table 1 — Example of main indicators for benefit evaluation of reclaimed water use
Category Indicators
Resource benefit Conventional water resource savings, energy, carbon, and phosphorous resource recovery, etc.
Ecological and
Reduction of contaminants, electricity use, greenhouse gas (GHG) emissions, and achievement
environmental
of E-flows, ecosystem protection/restoration, etc.
benefit
Social benefit Improvement of local natural environment, improvement of regional natural environment, etc.
Economic benefit Avoided cost, net present value (NPV), internal rate of return (IRR), etc.
6.2 Resource benefits
6.2.1 Conventional water resource savings
Reclaimed water can be an alternative water resource for many activities that do not require potable water
quality. The amount of conventional water resource (i.e. surface water, rivers and lakes and groundwater
that are naturally available) savings due to the substitution by reclaimed water and other water-saving
activities can be calculated using Formula (1):
QA=−Q (1)
t1 s
where
A is the amount of conventional water resource savings, expressed in m ;
Q is the amount of reclaimed water use, expressed in m ;
t
Q is the amount of water savings from water-saving activities and measures, expressed in m .
s
6.2.2 Energy resource recovery
Reclaimed water contains energy resources which can be further extracted and utilized. The amount of
energy (heat or cold) resource recovery during water reclamation and reuse processes can be calculated
using Formula (2):
AQ=×ρ××ΔtC
2w
A ×F
A = (2)
c
F1+
A ×H
A =
h
H1−
where
A is the amount of heat or cold energy recovered during water reclamation and reuse processes, ex-
pressed in kJ;
Q is the amount of reclaimed water used during the process, expressed in m ;
w
ρ is the density of reclaimed water, expressed in kg/m ;
Δt is the temperature difference of extracted reclaimed water, expressed in °C;
C is the specific heat capacity of reclaimed water, 4,19 kJ/(kg·°C);
A is the amount of cold energy output of the reclaimed water heat pump system, expressed in kJ;
c
A is the amount of heat energy output of the reclaimed water heat pump system, expressed in kJ;
h
F is the performance coefficient of reclaimed water heat pump unit for cooling;
H is the performance coefficient of reclaimed water heat pump unit for heating.
6.2.3 Carbon resource recovery
Reclaimed water contains carbon resources which can be further extracted and utilized. The amount of
carbon resource recovery during water reclamation and reuse processes can be calculated using Formula (3):
n
AA= (3)
33∑ ,i
i=1
where
A is the amount of carbon resource recovery during water reclamation processes (e.g. sedimentation,
3,i
settling and fermentation processes) via physical separation, hydrolysis and/or fermentation ap-
proaches, expressed in kg COD;
n is the number of water reclamation processes with carbon resource extraction and recovery.
6.2.4 Phosphorous resource recovery
Reclaimed water contains phosphorous resources which can be further extracted and utilized. The amount
of phosphorous resource recovery during water reclamation and reuse processes can be calculated using
Formula (4):
n
AA= (4)
44,i
∑
i=1
where
A is the amount of phosphorous resource recovery during water reclamation processes (e.g. biological
4,i
treatment and anaerobic digestion processes) via the formation of struvite, hydroxyapatite, etc.,
expressed in kg;
n is the number of water reclamation processes with phosphorous resource extraction and recovery.

6.3 Ecological and environmental benefits
6.3.1 Reduction of contaminants
Reclaimed water use can reduce the contaminant loading that was sourced from the wastewater directly
discharging into receiving water bodies. Reduction of contaminants due to the substitution of direct
wastewater discharge by reclaimed water use can be calculated using Formula (5):
BQ=×(CC− )/1000 (5)
1,jjtw, j, r
where
th
B is the reduction in j contaminant loading, expressed in kg;
1,j
Q is the amount of reclaimed water use, expressed in m ;
t
th
C is the concentration of j contaminant of the wastewater discharge (average concentration, monthly
j,w
mean or annual mean), expressed in mg/l;
th
C is the concentration of j contaminant of reclaimed water (average concentration, monthly mean or
j,r
annual mean), expressed in mg/l.
NOTE For other water reuse applications, other formulae or calculation m
...