Chapter A6.4. Measurement of pH

Techniques and Methods 9-A6.4



The “National Field Manual for the Collection of Water-Quality Data” (NFM) provides guidelines and procedures for U.S. Geological Survey (USGS) personnel who collect data used to assess the quality of the Nation’s surface-water and groundwater resources. This chapter, NFM A6.4, provides guidance and protocols for the measurement of pH of a water sample, which include the scientific basis of the measurement, selection and maintenance of equipment, calibration, procedures for measurement and reporting, and troubleshooting. It updates and supersedes USGS Techniques of Water-Resources Investigations, book 9, chapter A6.4, version 2.0, by G.F. Ritz and J.A. Collins. The pH of natural waters is routinely measured when water samples are collected, is often measured continually at USGS streamgages, and is a parameter regularly measured during laboratory and field experiments. The field methods for measuring pH described in this chapter are applicable to most natural waters.

Before 2017, the NFM chapters were released in the USGS Techniques of Water-Resources Investigations series. Effective in 2018, new and revised NFM chapters are being released in the USGS Techniques and Methods series; this series change does not affect the content and format of the NFM. More information is in the general introduction to the NFM (USGS Techniques and Methods, book 9, chapter A0) at The authoritative current versions of NFM chapters are available in the USGS Publications Warehouse at Comments, questions, and suggestions related to the NFM can be addressed to

Suggested Citation

U.S. Geological Survey, 2021, Measurement of pH: U.S. Geological Survey Techniques and Methods, book 9, chap. A6.4, 21 p., [Supersedes USGS Techniques of Water-Resources Investigations, book 9, chap. A6.4, version 2.0.]

ISSN: 2328-7055 (online)

Table of Contents

  • Abstract
  • 1.0 Introduction
  • 2.0 Equipment and Supplies
  • 3.0 Maintenance and Preparation of pH Instruments
  • 4.0 Calibration of the pH Instrument System
  • 5.0 Measurement of pH
  • 6.0 Quality Assurance/Quality Control for Measurements of pH
  • 7.0 Reporting
  • 8.0 Troubleshooting
  • Acknowledgments
  • Selected References
Publication type Report
Publication Subtype USGS Numbered Series
Title Chapter A6.4. Measurement of pH
Series title Techniques and Methods
Series number 9-A6.4
DOI 10.3133/tm9A6.4
Year Published 2021
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) WMA - Laboratory & Analytical Services Division
Description vi, 21 p.
Larger Work Type Report
Larger Work Subtype USGS Numbered Series
Larger Work Title Section A: National field manual for the collection of water-quality data in Book 9: Handbooks for water-resources investigations
Public Comments Techniques and Methods 9-A6.4 supersedes Techniques of Water-Resources Investigations 09-A6.4, version 2.0.
Online Only (Y/N) Y
Additional Online Files (Y/N) N
Google Analytic Metrics Metrics page
Additional publication details