ISO 21413:2005

Overview

ISO 21413:2005 - "Manual methods for the measurement of a groundwater level in a well" - specifies standardized procedures and minimum accuracy requirements for manual groundwater level measurement in wells. The standard covers three manual methods - graduated steel tape, electric tape, and air-line - plus procedures for measuring flowing (overflowing) wells and for establishing a permanent measuring point. ISO 21413:2005 explicitly excludes automated electrical or mechanical logging systems.

Key topics and requirements

• Measurement methods: Detailed procedures for the graduated steel tape (wetted-tape), electric tape (contact-sensor), and air-line (pressurized tube) methods.
• Flowing well procedures: Techniques and accuracy considerations for measuring water levels in wells that discharge at the ground surface.
• Permanent measuring point (MP): Steps to establish and document a stable reference point on the well casing and relate it to land-surface datum.
• Accuracy requirements:
  • Independent steel tape measurements should agree within ±1.0 cm for depths < 60 m.
  • For depths between 60 m and 150 m, agreement within ±2.0 cm is required.
  • Guidance on deep-well corrections (thermal expansion, tape stretch) is provided in Annex A; Annex B covers air-line corrections.
• Calibration & maintenance: Steel tapes should be calibrated at least annually against a reference tape; records of calibration and maintenance must be kept.
• Data recording: The standard prescribes minimum data recording elements (measuring point, MP correction to land-surface datum, raw readings, method used, and notes on assumptions or corrections).
• Advantages and limitations: Discussion of method-specific pros/cons (e.g., steel tape accuracy vs. susceptibility to condensation; air-line use for inaccessible wells).
• Assumptions: Clear listing of assumptions such as plumbness of casing, availability of prior measurements, and condition of measuring devices.

Applications

ISO 21413:2005 is practical for:

• Groundwater monitoring programs (routine water-level surveys)
• Environmental site assessments and remediation monitoring
• Hydrogeological investigations and well inventory surveys
• Water utilities and well owners needing standardized manual measurement protocols

Using ISO 21413 ensures consistent, comparable water-level data, facilitates quality control, and documents measurement uncertainty for regulatory reporting, research and long-term monitoring.

Who should use it

• Hydrogeologists and field technicians
• Environmental consultants and regulators
• Water-resource managers and utilities
• Well contractors and monitoring program coordinators

Related standards and context

ISO 21413 was prepared by ISO/TC 113 (Hydrometry), Subcommittee SC 8 (Groundwater). For a broader hydrometry framework, consider other ISO hydrology/hydrometry documents produced by the same technical committee.

Keywords: ISO 21413, groundwater level measurement, water-level measurement in wells, manual water-level methods, graduated steel tape, electric tape, air-line method, flowing well measurement, well monitoring standards.