ISO 25175:2026

Marine technology — Standard test methods for performance of reverse osmosis (RO) and nanofiltration (NF) membrane elements

This document provides test methods for determining air tightness and separation performance (permeation and salt rejection) of reverse osmosis (RO) and nanofiltration (NF) membrane elements.

Technologie maritime — Méthodes d’essai normalisées pour les performances des éléments de membranes d’osmose inverse (OI) et de nanofiltration (NF)

General Information

• Status: Published
• Publication Date: 24-Jun-2026
• ICS: 13.060.20 - Drinking water
• Technical Committee: ISO/TC 8/SC 13 - Marine technology
• Drafting Committee: ISO/TC 8/SC 13/WG 3 - Seawater desalination
• Current Stage: 6060 - International Standard published
• Start Date: 25-Jun-2026
• Due Date: 08-Jul-2027
• Completion Date: 25-Jun-2026

Overview

ISO 25175: Marine technology - Standard test methods for performance of reverse osmosis (RO) and nanofiltration (NF) membrane elements establishes internationally recognized procedures for evaluating the performance of RO and NF membranes. Developed by ISO/TC 8/SC 13 (Marine Technology), this standard is crucial for seawater desalination and water treatment industries. It defines standardized methods to test air tightness, water production, membrane permeation, and salt rejection, as well as the specification of test solutions and conditions. By providing clear criteria, ISO 25175 eliminates inconsistencies in performance evaluation, enabling reliable comparisons and informed selection of membrane elements for diverse marine and industrial applications.

Key Topics

• Normalized Test Conditions: ISO 25175 specifies detailed conditions for testing, including:
  • Composition of test solutions
  • Operating pressure
  • Temperature
  • pH levels
  • Recovery rates
• Performance Metrics: The evaluation of membrane elements includes key indicators:
  • Water production rate
  • Membrane permeation (flux)
  • Salt rejection (purity of produced water)
• Test Procedures: The standard outlines steps for:
  • Air tightness verification using vacuum decay test methods
  • Performance tests covering apparatus setup, sample collection, and data recording
  • Accurate analysis and reporting of test results
• Applicable Membrane Types: Coverage includes spiral wound and hollow fiber configurations for:
  • Seawater RO (SWRO)
  • Brackish water RO (BWRO)
  • Low pressure RO (LPRO)
  • Nanofiltration (NF) elements

Applications

ISO 25175 supports a wide range of marine and industrial applications, providing significant practical benefits:

• Seawater Desalination: Ensures reliable evaluation of RO and NF membranes used to convert seawater to fresh water, critical for ships, offshore platforms, and coastal municipalities.
• Brackish and Wastewater Treatment: Enables standardized performance measurement for membranes treating brackish water or reclaiming industrial wastewater.
• Product Comparison and Procurement: Facilitates fair comparison of membrane elements from multiple manufacturers, supporting procurement decisions and regulatory compliance.
• Research and Development: Provides a common test framework for researchers evaluating new membrane materials or system designs.
• Performance Reporting: Mandates clear, consistent reporting, essential for project documentation, quality assurance, and technical communication among stakeholders.

By implementing ISO 25175, marine technology practitioners, engineers, membrane manufacturers, and water utilities can ensure consistent product quality and reduce technical barriers to trade and technology adoption.

Related Standards

• ISO 10523: Water quality - Determination of pH
• ASTM D5907: Standard Test Methods for Filterable Matter (Total Dissolved Solids) and Nonfilterable Matter (Total Suspended Solids) in Water
• ISO 14001: Environmental management systems - Requirements with guidance for use (for environmental impact assessments in water processing)
• ISO 16290: Space systems - Definition of the Technology Readiness Levels (for technology development and deployment stages)
• IEC Electropedia and ISO Online Browsing Platform: For terminology consistency in standardization

Keywords: ISO 25175, marine technology, reverse osmosis (RO), nanofiltration (NF), membrane performance testing, desalination, water treatment, salt rejection, water production, membrane permeation, standard methods, membrane elements, standard test procedures, seawater desalination, ISO standards, water quality standards.

Standards Content (Sample)

International
Standard
ISO 25175
First edition
Marine technology — Standard test
2026-06
methods for performance of reverse
osmosis (RO) and nanofiltration
(NF) membrane elements
Technologie maritime — Méthodes d’essai normalisées pour les
performances des éléments de membranes d’osmose inverse (OI)
et de nanofiltration (NF)
Reference number
© ISO 2026
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 RO and NF membrane elements types . 1
5 Membrane elements air tightness test . 1
5.1 General .1
5.2 Apparatus .2
5.3 Test procedure .2
6 Membrane elements performance test . 3
6.1 Apparatus .3
6.2 Test Solution .4
6.3 Test procedure .4
7 Calculation . 5
7.1 Water production .5
7.2 Membrane permeation .6
7.3 Salt rejection .6
7.4 Average salt rejection .6
8 Test report . 6
Annex A (informative) Example of a test report . 8
Bibliography . 9

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
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with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
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www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 8, Ships and marine technology, Subcommittee
SC 13, Marine technology.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
Introduction
Membrane elements are key components in seawater desalination. The diversity of application scenarios
and the complexity of feed-water quality in seawater desalination give rise to requirements for the flexibility
and diversity of membrane elements. Therefore, there are currently many types of membrane elements on
the market. The comparison and use of membrane components mainly refer to the product manual, but
the testing methods for membrane elements of different brands are not the same, which inevitably brings
obstacles to the users and researchers. For instance, performance evaluations of the same type of membrane
elements are obtained from different testing methods, making the comparison of these membrane elements
inaccurate.
To solve this problem, this document establishes test methods for evaluating the performance of membrane
elements used in seawater desalination, with a focus on reverse osmosis (RO) and nanofiltration (NF)
elements. It specifies the types of membrane elements to be tested and standardizes the corresponding
testing conditions. The document also covers the required test equipment, procedures, and data processing
methods. By providing a uniform benchmark, it serves as a standard reference for users in desalination
and related industrial applications, particularly in water treatment. This aims to facilitate the selection of
membrane elements and enhances clarity in technical communication.

v
International Standard ISO 25175:2026(en)
Marine technology — Standard test methods for performance
of reverse osmosis (RO) and nanofiltration (NF) membrane
elements
1 Scope
This document provides test methods for determining air tightness and separation performance (permeation
and salt rejection) of reverse osmosis (RO) and nanofiltration (NF) membrane elements.
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 10523, Water quality — Determination of pH
3 Terms and definitions
No terms and definitions are listed in this document.
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 RO and NF membrane elements types
The following membrane elements are covered in this document.
— Seawater desalination RO (SWRO) membrane elements
— Brackish water RO (BWRO) membrane elements
— Low pressure RO (LPRO) membrane elements
— NF membrane elements
This includes membrane elements with the following configurations.
— Spiral wound
— Hollow fibre
5 Membrane elements air tightness test
5.1 General
The membrane performance test shall be performed after passing the air tightness test.

5.2 Apparatus
Air tightness of the membrane elements shall be tested using the vacuum decay test (VDT) method. A
diagram of the apparatus is depicted in Figure 1.
Key
1 stopper
2 membrane element
3 valve A
4 valve B
5 vacuum pressure gauge
6 valve C
7 water trap
8 vacuum pump
vacuum degree
Figure 1 — Apparatus for testing air tightness of membrane elements
5.3 Test procedure
The following steps apply for testing spiral wound membrane elements.
a) Fully wet the membrane.
b) Open valve A to drain the water trapped in membrane element, then seal one end of the permeate
collection tube and close valve A.
c) Connect the other end of the membrane element to the vacuum pressure gauge, open valve B and valve C
and start the vacuum pump.
d) Close val
...