Overview
ISO 10523:2008 - "Water quality - Determination of pH" defines an electrometric method for measuring the pH of a wide range of water matrices using pH glass electrodes. The standard covers measurements in rain, drinking and mineral waters, bathing waters, surface and ground waters, municipal and industrial waste waters, liquid sludge and similar samples. Measurement range is pH 2 to pH 12, for ionic strength below I = 0.3 mol/kg (conductivity γ < 2 000 mS/m) and temperatures between 0 °C and 50 °C. The document includes procedural requirements, sampling guidance and informative annexes on buffer preparation, field and flow-system measurements, low ionic strength waters and performance data.
Key topics and technical requirements
- Measurement principle: electrometric determination using a pH glass electrode and reference electrode; temperature must be recorded with the pH reading.
- Calibration: use of certified buffer solutions (or in-house buffer preparation per Annex A when necessary); meters must allow offset (zero), slope and temperature adjustment.
- Apparatus requirements: pH meter resolution of 0.01 pH or better; meter must permit display in pH or voltage and provide adjustment functions (document specifies input resistance > 10 Ω).
- Electrodes: glass measuring electrode and appropriate reference electrode (liquid-filled, gel or polymer electrolytes as applicable); attention to electrode slope and zero-point.
- Sampling and handling: minimize gas exchange (fill bottles bubble-free), store samples cool (2–8 °C) and dark, and measure as soon as possible to avoid pH shifts.
- Interferences and quality control: addresses membrane coatings, diaphragm blockages, diffusion voltages in low-conductivity waters, CO2 degassing effects, suspended solids, and ageing of electrodes. Annexes provide procedures for field measurement, flow systems and low ionic strength samples.
Applications and practical value
ISO 10523:2008 is used to ensure accurate, traceable pH measurements in:
- Drinking water compliance testing and distribution monitoring
- Environmental monitoring of rivers, lakes and groundwater
- Wastewater and sludge treatment process control
- Industrial effluents and process water quality control
- Research labs requiring standardized pH data
Practical benefits include improved comparability of pH results, guidance on minimizing measurement errors (temperature, ionic strength, electrode maintenance) and clear sampling best practices.
Who should use this standard
- Water and wastewater laboratories
- Environmental monitoring agencies
- Drinking water utilities and treatment operators
- Industrial quality/control laboratories
- Instrument manufacturers and field technicians
Related standards
Keywords: ISO 10523:2008, pH determination, water quality, pH measurement, pH electrode, buffer solutions, sampling, ionic strength, field measurement.
