ISO 23446:2021

Overview

ISO 23446:2021 is a global standard developed by the International Organization for Standardization (ISO) that provides comprehensive guidelines for the product water quality of seawater reverse osmosis (RO) desalination, specifically for municipal water supply. As urbanization and climate change exacerbate freshwater scarcity worldwide, seawater desalination using RO technology has become a crucial solution to ensure reliable and sustainable potable water sources.

This standard defines essential water quality parameters, testing methods, and monitoring frequencies to guarantee that the treated water is compatible with municipal distribution pipelines and infrastructure. It addresses potential issues such as water aggressiveness towards metallic materials and emphasizes post-treatment procedures to stabilize mineral content.

Key Topics

• Water Quality Parameters: The standard specifies critical parameters including pH, calcium hardness, total alkalinity, total dissolved solids (TDS), and the Langelier Saturation Index (LSI) to assess water stability and corrosiveness.

• Parameter Ranges:

  • pH: 7.5 to 8.5 (with tighter ranges recommended for specific cases)
  • Calcium hardness: 60 to 120 mg/l as CaCO₃
  • Total alkalinity: ≥ 50 mg/l as CaCO₃
  • TDS limits for desalted water vary by RO process type (single or double pass)
  • LSI: between -0.5 and 0.5 to ensure balanced scaling and corrosion potential

• Monitoring Frequency:

  • Desalted water parameters such as electrical conductivity and pH are to be monitored daily.
  • Product water quality parameters like calcium hardness and total alkalinity require weekly or monthly sampling depending on local contexts.
  • Enhanced frequency is recommended for well-equipped plants supplying primary municipal water sources.

• Test Methods:

  • pH measurement conforms to ISO 10523.
  • Electrical conductivity tests follow ISO 7888.
  • Calcium hardness determined via ISO/TS 15923-2 with specific calculation methods.
  • Total alkalinity assessed according to ISO 9963-1.
  • TDS determined by EN 15216-2007.
  • LSI calculation is detailed within the standard.

• Post-Treatment Importance: Due to the low mineral content and high corrosiveness of raw RO-desalinated water, the standard advocates mineral addition or blending to achieve balanced water chemistry.

Applications

ISO 23446:2021 serves as a critical reference for various stakeholders in the marine and municipal water supply sectors, including:

• Water Engineers and Operators: To design, monitor, and operate seawater RO desalination plants ensuring product water meets municipal supply criteria.

• Municipal Water Authorities: To develop water quality control frameworks that protect infrastructure from corrosion and scaling.

• Environmental and Public Health Agencies: To define safe deployment of desalinated water within urban water systems, considering public health and system longevity.

• Manufacturers and Suppliers: To calibrate equipment and sensors for compliance with standardized test methods and monitoring requirements.

• Policy Makers and Regulators: To set regulatory limits and water quality standards based on internationally recognized guidelines.

Implementing the guidelines can enhance the durability of water distribution pipelines, reduce maintenance costs, and assure safe drinking water quality derived from seawater RO desalination.

Related Standards

Key international standards complementing ISO 23446:2021 include:

• ISO 10523: Water quality - Determination of pH
• ISO 7888: Water quality - Electrical conductivity measurement
• ISO/TS 15923-2: Water quality - Photometric determination of selected parameters including calcium
• ISO 9963-1: Water quality - Total alkalinity determination
• EN 15216-2007: Determination of total dissolved solids (TDS) in water
• WHO Guidelines for Drinking-Water Quality: Global health recommendations impacting water treatment standards

These allied standards ensure harmonized testing procedures and coherent quality assessment methodologies relevant to water treatment and supply.

Keywords: ISO 23446, seawater reverse osmosis, RO desalination, municipal water supply, water quality guidelines, water parameters, desalinated water, calcium hardness, Langelier saturation index, TDS, water monitoring frequency, marine technology, post-treatment water quality, water pipeline compatibility, corrosion control in water systems.