ISO/FDIS 18998

ISO/DISFDIS 18998:2025(en)
ISO/TC 282/SC 2/WG 4
Secretariat: SAC
Date: 2025-08-1810-09
Water reuse in urban areas — Guidelines for decentralized water
reuse system — Management of a decentralized water reuse system
FDIS stage
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ISO/DISFDIS 18998:2025(en)
Contents
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Management models of decentralized water reuse systems . 1
4.1 General . 1
4.2 Management models . 3
4.3 Management process . 8
5 Management of source water . 9
6 Management of treatment processes for water reuse . 10
6.1 General . 10
6.2 Selection of monitoring indicators . 10
6.3 Process adjustment . 11
6.4 Operation and maintenance of equipment . 11
7 Management of storage system . 12
8 Management of distribution system . 12
9 Management of end uses . 13
9.1 Principles . 13
9.2 Main items of end uses . 13
10 Management of sludge treatment . 14
10.1 General . 14
10.2 Generation and collection . 14
10.3 Selection and design . 14
10.4 Monitoring and control . 15
10.5 Safety and environmental measures . 15
10.6 Quality control and evaluation . 15
11 Management of monitoring . 15
11.1 General . 15
11.2 Baseline monitoring . 15
11.3 Validation monitoring . 15
11.4 Operational monitoring . 16
11.5 Verification monitoring . 17
12 Management of incidents and emergencies . 19
13 Management of operations and maintenance staff . 20
14 Review . 20
Bibliography . 21

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.
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ISO/DISFDIS 18998:2025(en)
Introduction
With economic development, climate change, population growth, and rapid urbanization continuing to shape
the world, water has become an increasingly important strategic resource, particularly in arid and semi-arid
regions. However, even in areas with abundant water resources, challenges such as water shortages and
seasonal water scarcity remain. Water scarcity is recognized as one of the most serious threats to sustainable
development. To address these challenges, an increasing number of communities are turning to use reclaimed
water to meet water needs. This approach has been shown to be effective in improving the reliability of long-
term water supply, particularly in areas where water is scarce.
While centralized water reuse facilities have been widely implemented under different ownership and
management structures, there is also a need to develop decentralized/onsite water reuse systems in cost-
effective and resource-efficient ways, which can improve flexibility and convenience. Decentralized water
reuse systems have emerged as an essential component of water management in many cities and countries.
These systems typically consist of source water collection, wastewater treatment facilities, storage and
distribution systems, and monitoring systems. Management concepts and principles should be implemented
from source water to end users throughout the system, and appropriate strategies should be adopted for each
component.
This document provides management concepts and principles for decentralized water reuse systems in urban
areas, and it can be used by practitioners and regulatory authorities, who intend to implement management
concepts, principles, and supports on decentralized water reuse in a safe, reliable, and sustainable manner. It
considers and addresses key issues in the management process, which can help relevant practitioners and
users to adopt cost-effective methods to achieve safe, reliable, and appropriate reuse of reclaimed water. For
detailed information on the design of decentralized water reuse systems, refer to ISO 23056.
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DRAFT International Standard ISO/DIS 18998:2025(en)

Water reuse in urban areas — Guidelines for decentralized water
reuse system — Management of a decentralized water reuse system
1 Scope
This document provides guidelines for the management of decentralized water reuse systems and water reuse
applications in urban areas.
This document addresses decentralized water reuse systems in their entirety and is applicable to any water
reuse systems component (e.g. reclaimed water, source water, treatment, storage, distribution, operation and
maintenance, and monitoring).
This document covers:
— — management of each system component of a decentralized water reuse system;
— — specific aspects for consideration and emergency response.
This document does not cover monitoring parameters and regulatory values of a decentralized water reuse
system.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitute
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 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/
4 Management models of decentralized water reuse systems
4.1 General
Effective management practices are indispensable for the successful reuse of treated wastewater in
decentralized water reuse systems. The management of decentralized water reuse systems should consider
the following aspects:
— — source water assessment;
— — system design;
— — location selection;
— — operations and maintenance;
— — regulatory compliance;
— — cost-benefit analysis and;
— — community engagement.
Decentralized water reuse management should align with utilization systems through various management
models, including onsite, cluster, and community models. Risk management and control should be highlighted
in decentralized water reuse systems. Aspects and specific points that should be considered in the
management of decentralized water reuse systems are shown in Table 1Table 1.
Table 1 — Considerations for management of decentralized water reuse systems
Primary aspects Contributing factors
— — Water quantity monitoring
— — Water quality testing
Water quality and quantity
— — Monitoring equipment
— — Equipment maintenance
— — Troubleshooting
— — Waste removal and disposal
Operations and maintenance
— — Leak detection and contamination control
— — System regular check and maintenance
— — Odour control
— — Operational costs
— — Capital cost
— — Sustainability
— — Tax policies
Economic impact
— — Revenue and risk
— — Reclaimed water pricing
— — System operation efficiency
— — Regulations
— — Occupational health and safety standards
Legal compliance
— — Permits and applications
ISO/DISFDIS 18998:2025(en)
Primary aspects Contributing factors
— — Responsibilities
— — Monitoring and compliance
— — Effluent standards
— — Public acceptance
— — Water resource conservation
Social impact
— — Environmental protection
4.2 Management models
4.2.1 Onsite systems Managementmanagement model
Onsite systems are used to treat wastewater generated from family/household-based systems and onsite
building scale systems. The onsite systems are usually managed and maintained by household owners or users
(Figure 1(Figure 1).). This model offers flexibility, autonomy, and cost savings. Wastewater collection,
treatment, and use should align with water demands, adapting processes in less developed areas while
prioritizing users’ health. The implementation of management initiatives should also consider users' economic
ability and appropriate technology. For instance, onsite water reuse systems can be improved with
autonomous controls that use Internet of Things (IoT) and sensors to manage water quality accurately, and
user involvement remains crucial to prevent pollution and maintain compliance with water quality standards.
Key
ISO/DISFDIS 18998:2025(en)
1 onsite systems
2 wastewater treatment
3 water reclamation
4 end uses
Figure 1 — Onsite systems management model
4.2.2 Cluster systems Managementmanagement model
Cluster systems are designed to treat the wastewater from a collection of dwellings or facilities located
adjacent to each other with typically a few owners. The cluster systems are normally used for managing
multiple end uses through a unified wastewater treatment and water reclamation process (Figure 2(Figure
2).). This enables information sharing, resource integration, and optimization to improve water reuse
efficiency and economic benefits. Real-time monitoring and control enhance system stability and security,
while unified management strategies optimize operations. However, this model requires more financial and
technical resources, as well as resilience to single-point of failure. Coordination among subsystems is also
crucial.
Key
1 cluster systems
2 wastewater treatment
3 water reclamation
4 end uses
ISO/DISFDIS 18998:2025(en)
Figure 2 — Cluster systems management model
NOTE The treatment process shown in Figure 2Figure 2 is only an example of processes listed in ISO 24521.
4.2.3 Community systems Managementmanagement model
The community systems management model includes wastewater collection and treatment, as well as
reclaimed water storage and distribution through planning, implementation, monitoring, and evaluation
(Figure 3(Figure 3).). This management model is relatively complex and requires professional system
management (such as automatic control systems, remote control, etc.)) to achieve sustainability. It improves
water utilization and increases economic benefits, while reducing dependence on natural resources and
pollution load. However, it faces problems such as high operations and maintenance costs, technical
difficulties, and communication problems.

Key
1 community systems
2 wastewater treatment
3 water reclamation
4 end uses
Figure 3 — Community systems management model
4.3 Management process
The management process of decentralized water reuse systems is crucial for ensuring stable operation, water
quality safety, and efficient utilization. A comprehensive and efficient management system covers source
water collection, treatment technology, storage and distribution, end uses, etc. (Table 2(Table 2).).
Table 2 — Management process of decentralized water reuse systems
Management process Considering elements
— — Water quality
— — Water quantity
Source water collection
— — Routine checking
— — Evaluation indicator
Treatment technology
ISO/DISFDIS 18998:2025(en)
Management process Considering elements
— — Potential treatment technologies
— — Regular operation checking
— — Regular monitoring of the water quality
— — System operation
— — Objectives
Storage and distribution
— — Methods for quality &and quantity control
— — Routine checking of operations and maintenance
— — Operability
End uses
— — Safety, quantity & quality
— — Treatment
— — Disposal
Sludge
— — Possible reuse options
— — Safety, quality and quantity checking
— — Frequency of monitoring
— — Data recording, keeping, corrective action
Monitoring
— — Improvement actions related to monitoring report
— — Identification
— — Prevention
Incidents and emergencies
— — Verification
— — Recording, reporting, and taking action
— — Awareness
— — Training
Stakeholder
— — Public outreach
5 Management of source water
Management of source water in decentralized water reuse systems depends on different scenarios and types
of source water. For instance, the management of source water for onsite and cluster systems is primarily the
responsibility of end users, whereas the source water management for community systems are more
frequently carried out by authorized practitioners.
Management of source water focuses on source water quality and quantity. In terms of source water quality,
it is recommended that the management practices align with those of the facility to measure and monitor the
quality of source water. For example, an early warning system couldcan be incorporated into the program to
facilitate the provision of timely information for the detection of sudden changes in source water quality. At
the same time, contaminant concentrations and the various alternatives for diverting the contaminated waters
are also important toshould be documented in the source water control program. Accordingly, informed
decisions or responses can be made with regards to changing the treatment and operational methods or
closing the intakes for the source control programs.
Information on the quantity of source water should be monitored and recorded in a timely manner in order
to maintain the water balance between source water and reclaimed water. Furthermore, a response and
management plan for mitigating reclaimed water shortages may be developed and maintained based on the
importance of reclaimed water supply to end users. The plan should include strategies for the provision of
alternative water resources for the provision of essential services on a short-term basis. An additional
consideration that should be included in the plan is whether availability of the reclaimed water would only be
on a seasonal or interruptible basis, or alternatively. Alternatively, a clear time schedule for the period of
delivery should be included.
6 Management of treatment processes for water reuse
6.1 General
An indispensable component of managing treatment processes for water reuse is a comprehensive
performance monitoring plan, including monitoring indicators, process adjustment, and operation and
maintenance of equipment. This plan serves a vital role in validating both the operation normality and
effectiveness of the treatment processes, and the conformity of reclaimed water with purpose criteria.
6.2 Selection of monitoring indicators
6.2.1 Principles of indicator selection
Monitoring indicators are essential for ensuring the proper functioning of decentralized water reuse systems,
and also help to achieve the desired outcomes. The following are principles for selecting monitoring indicators
for decentralized water reuse systems.
a) a) The water quality and water quantity demands of end users should be considered, including
the process operational indicators specified in the relevant water quality standards.
b) b) The indicators should meet local environmental protection and water reuse standards should
be ensured to meetensure the safety and hygiene of the reclaimed water quality.
c) c) EasyThe indicators should be easy to measure, and appropriate responses can be made
accordingly.
d) d) The treatment processes’ effectiveness and efficiency should be demonstrated through real-
time indications of process performance.
e) e) EnsureIt should be ensured that the operating and construction costs of the system are
reasonable.
f) f) System design and equipment selection should complyconform with local technical standards
and building codes.
The treatment processes for water reuse include natural treatment processes, aerobic, anaerobic, and
combined processes, disinfection, etc. A detailed description of water treatment processes is provided in
ISO 24521. Furthermore, advanced treatment technologies are necessary when terminal reclaimed water
criteria become stricter. Different treatment processes have some commonalities in the selection of operating
ISO/DISFDIS 18998:2025(en)
indicators, such as common water quality indicators (e.g. Chemical Oxygen Demandchemical oxygen demand
(COD), Biochemical Oxygen Demandbiochemical oxygen demand (BOD), Total Nitrogentotal nitrogen (TN),
Total Phosphorustotal phosphorus (TP), Escherichia coli, etc.)) and water quantity indicators. related
standards. Technical assessment can refer to ISO 20761, ozone treatment technology can refer to
ISO20468ISO 20468-3, UV disinfection technology can refer to ISO20468ISO 20468-4, membrane filtration
technology can refer to ISO20468ISO 20468-5, ion exchange and electrodialysis technology can refer to
ISO20468ISO 20468-6, and advanced oxidation process technology can refer to ISO20468ISO 20468-7.
6.2.2 Indicator monitoring
Indicator monitoring is crucial to ensure the stable and efficient operation of decentralized water reuse
systems and the effective utilization of reclaimed water, and it should consider the following aspects:
a) a) Digital and physical continuous monitoring equipment should be calibrated, as this is essential
to ensure an adequate monitoring frequency for selected indicators, enabling the timely detection of
water quality issues and process anomalies.
b) b) Minimum parameters for necessary routine and rapid water quality tests, and minimum
frequency of water quality tests should be specified.
c) c) Regular assessments of system status should be performed, such as analysing data changes of
water quality and quantity to determine whether there are leaks or blockages, which can result in water
loss /or cross contamination.
d) d) Online and continuous monitoring equipment should be calibrated and regularly maintained
in accordance with the specified calibration schedule to guarantee precise and reliable operation.
e) e) A comprehensive monitoring system should be established to provide real-time monitoring
and feedback through monitoring data. Remote monitoring technologies such as sensors and the Internet
of ThingsIoT can be used to improve monitoring efficiency and timeliness.
6.3 Process
...