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Biological Oxygen Demand (BOD) is one of the most widely used indicators of water quality, measuring the level of biodegradable organic pollution in surface waters. In India, BOD has an enforceable statutory threshold of ≤ 3 mg/L, as notified under the Primary Water Quality Criteria for Bathing Waters (2000), and forms the legal basis for assessing pollution in rivers, lakes, and other surface waterbodies. This page briefly explains BOD and its regulatory significance.
What is Biological Oxygen Demand (BOD)?
Biological Oxygen Demand (BOD) is one of the most widely used indicators of water quality. It measures the level of biodegradable organic pollution in a waterbody.
BOD indicates the amount of dissolved oxygen consumed by microorganisms while decomposing organic matter in surface water. Higher BOD values mean more oxygen is being used, leaving less available for aquatic life, and therefore indicate higher levels of pollution.
How is BOD measured?
BOD is measured biologically by:
- Collecting a water sample
- Incubating it for a fixed period (usually 3 or 5 days)
- Measuring the amount of oxygen consumed by microorganisms as they break down organic matter
What is the Regulatory Threshold for BOD in India?
The Ministry of Environment and Forests’ Gazette Notification (2000) on Primary Water Quality Criteria for Bathing Waters is the only enforceable statutory standard that specifies a limit for Biological Oxygen Demand (BOD) in surface waters. It defines bathing-quality water as having a BOD of ≤ 3 mg/L, and this threshold is legally used to assess organic pollution in rivers and other surface waterbodies.
This enforceable statutory threshold is the basis for national assessments of polluted river stretches by Central Pollution Control Board
Also Read | All about Polluted River Stretches based on BOD
FAQ: Is BOD used to assess drinking water Quality?
No. While organic contamination can occur in drinking water, BOD is not used to assess drinking water quality under the BIS 10500:2012 Drinking Water Specification. BOD is designed to measure ongoing organic pollution in natural surface waters, such as rivers and lakes.
Treated drinking water is instead regulated using microbiological indicators, such as E. coli and total coliforms, which directly indicate direct public health risk and treatment failure.
