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Document ID ca-gcdwqgtd-2014-02-05-4 Title Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Turbidity URL https://www.canada.ca/en/health-canada/services/publications/healthy-living/guidelines-canadian-drinking-water-quality-turbidity/page-6-guidelines-canadian-drinking-water-quality-turbidity.html Jurisdiction /ca Subdomain(s) Drinking water, Analytical methods Language en Status completed Analyzed at 2026-03-17 14:41:00.892405+00:00 Relevance Provides approved analytical methods for turbidity monitoring in drinking water.

16 Qualitative 42 Quantitative 15 Definitions

Q Qualitative Requirements (16)

Req ID	Category	Intent	Legal Status	Name	Subdomain(s)	Context	Conditions	Confidence
#Q001	monitoring	operational	recommended	Turbidimeter Method Conformity	drinking water	Utilities should use turbidimeters that conform to one of the methods discussed below when monitoring drinking water.	When monitoring drinking water	high
#Q002	operational	operational	recommended	Turbidimeter Operation and Maintenance Programs	drinking water	Utilities should ensure that the appropriate operation, maintenance and calibration programs are in place for all turbidimeters.		high
#Q003	operational	operational	recommended	Turbidimeter Operating Procedures	drinking water	For example, all utilities should have operating procedures for cleaning turbidimeters, creating or using standards, sampling and calibrating turbidimeters.		high
#Q004	operational	operational	recommended	Online Turbidimeter Calibration Frequency	drinking water	It is recommended that utilities calibrate online turbidimeters at least quarterly, or more frequently if recommended by the manufacturer.	Applies to online turbidimeters	high
#Q005	operational	operational	recommended	Turbidimeter Calibration Verification and Re-calibration	drinking water	The calibration of turbidimeters should then be verified weekly with the appropriate standard and re-calibrated if the turbidimeter has drifted more than 10% from the value assigned to the standard.		high
#Q006	operational	operational	recommended	Turbidimeter Preventive Maintenance	drinking water	Preventive maintenance should also be part of a routine turbidimeter QA/QC program.		high
#Q007	operational	operational	recommended	QA/QC Interfering Factors Consideration	drinking water	Other factors, such as air bubbles, stray light, coloured water and particle contamination, should also be considered in QA/QC programs, as these can cause false high or low readings for turbidity		high
#Q008	monitoring	operational	recommended	Immediate Sample Analysis	drinking water	As the turbidity of a sample can change due to changes in temperature and particle flocculation and sedimentation, samples should be analyzed immediately		high
#Q009	monitoring	operational	recommended	On-site or Portable Sample Analysis	drinking water	It is recommended that samples be analyzed using on-site turbidimeters in the treatment plant or portable turbidimeters when conducting sampling in the field.	When analyzing samples in the treatment plant or field	high
#Q010	operational	operational	mandatory	Analyst Measurement Error Awareness	drinking water	analysts must be aware of the factors that can affect turbidity measurements and be careful to minimize potential sources of measurement error.		high
#Q011	operational	operational	mandatory	Low-Level Measurement Support and Training	drinking water	low-level turbidity measurement must be accompanied by careful instrument calibration and verification as well as comprehensive standard operating procedures, including rigorous analyst training		high
#Q012	reporting	reporting	recommended	Standard Method Reporting Precision	drinking water	All three methods state that turbidity readings should be reported to the nearest 0.05 NTU when the turbidity range is 0-1.0 NTU.	When turbidity range is 0-1.0 NTU using APHA 2130B, EPA 180.1, or GLI Method 2	high
#Q013	prohibition	operational	mandatory	Particle Counter Application Restriction	drinking water	Particle counters are restricted to performance verification only, and no limit is set as a maximum acceptable concentration for the number of particles in the treated water.		high
#Q014	reporting	reporting	recommended	ISO 7027 Reporting Precision	drinking water	ISO 7027 (ISO, 1999) indicates that results should be reported to the nearest 0.01 FNU when turbidity is below 0.99 FNU.	When turbidity is below 0.99 FNU using ISO 7027	high
#Q015	reporting	reporting	recommended	ASTM D6855-10 Reporting Precision	drinking water	Results should be reported to the nearest 0.01 NTU for water with turbidity of less than 1.0 NTU and to the nearest 0.05 NTU for water with turbidity between 1.0 and 5.0 NTU (ASTM International, 2010).	When measuring static turbidity using ASTM D6855-10	high
#Q016	reporting	reporting	recommended	ASTM D6698-07 Reporting Precision	drinking water	Results should be reported to the nearest 0.01 NTU for water with turbidity less than 1.0 NTU and to the nearest 0.1 NTU for water with turbidity between 1.0 and 5.0 NTU (ASTM International, 2007).	When measuring online turbidity using ASTM D6698-07	high

P Quantitative Requirements (42)

Req ID	Category	Intent	Legal Status	Name	Subdomain(s)	Limit Type	Limit Value	Context	Conditions	Confidence
#P001	operational	operational	recommended	Turbidity difference detection limit (U.S. EPA Method 180.1, GLI Method 2, APHA/AWWA/WEF Standard Method 2130B)	drinking water	requirement	<= 0.02 NTU	nephelometers designed under these methods should be able to detect turbidity differences of 0.02 NTU or less	in waters having a turbidity of less than 1.0 NTU	high
#P002	operational	reporting	recommended	Turbidity reporting resolution (U.S. EPA Method 180.1, GLI Method 2, APHA/AWWA/WEF Standard Method 2130B)	drinking water	requirement	0.05 NTU	turbidity readings should be reported to the nearest 0.05 NTU	when the turbidity range is 0-1.0 NTU	high
#P003	operational	reporting	recommended	Turbidity reporting resolution (ISO 7027)	drinking water	requirement	0.01 FNU	results should be reported to the nearest 0.01 FNU	when turbidity is below 0.99 FNU	high
#P004	operational	operational	recommended	Turbidity difference detection limit (ASTM D6855-10)	drinking water	requirement	<= 0.01 NTU	resolution of the instrument should permit detection of turbidity differences of 0.01 NTU or less	in waters with a turbidity of less than 5.0 NTU	high
#P005	operational	reporting	recommended	Turbidity reporting resolution (ASTM D6855-10)	drinking water	requirement	0.01 NTU	Results should be reported to the nearest 0.01 NTU	for water with turbidity of less than 1.0 NTU	high
#P006	operational	reporting	recommended	Turbidity reporting resolution (ASTM D6855-10) high range	drinking water	requirement	0.05 NTU	Results should be reported to the nearest 0.05 NTU	for water with turbidity between 1.0 and 5.0 NTU	high
#P007	operational	operational	recommended	Turbidity difference detection limit (ASTM D6698-07) low range	drinking water	requirement	<= 0.01 NTU	turbidity differences of 0.01 NTU or less should be detected	in water with a turbidity less than 1.0 NTU	high
#P008	operational	operational	recommended	Turbidity difference detection limit (ASTM D6698-07) high range	drinking water	requirement	<= 0.10 NTU	differences of 0.10 NTU or less should be detected	in waters with turbidity between 1.0 and 5.0 NTU	high
#P009	operational	reporting	recommended	Turbidity reporting resolution (ASTM D6698-07) low range	drinking water	requirement	0.01 NTU	Results should be reported to the nearest 0.01 NTU	for water with turbidity less than 1.0 NTU	high
#P010	operational	reporting	recommended	Turbidity reporting resolution (ASTM D6698-07) high range	drinking water	requirement	0.1 NTU	Results should be reported to the nearest 0.1 NTU	for water with turbidity between 1.0 and 5.0 NTU	high
#P011	operational	operational	recommended	Turbidity difference detection limit (Hach FilterTrak Method 10133)	drinking water	requirement	<= 1 mNTU	should permit the detection of a turbidity difference of 1 mNTU (0.001 NTU) or less	in waters having turbidities less than 5.0 NTU	high
#P012	operational	operational	recommended	Turbidimeter Calibration Drift Limit	drinking water	requirement	> 10 %	re-calibrated if the turbidimeter has drifted more than 10% from the value assigned to the standard	During weekly calibration verification	high
#P013	operational	operational	recommended	Online Turbidimeter Calibration Frequency	drinking water	requirement	>= 1 per quarter	Utilities should ensure that the appropriate operation, maintenance and calibration programs are in place for all turbidimeters.	for online turbidimeters; or more frequently if recommended by manufacturer	high
#P014	operational	operational	recommended	Online Turbidimeter Verification Frequency	drinking water	requirement	1 per week	The calibration of turbidimeters should then be verified weekly with the appropriate standard	re-calibrate if the turbidimeter has drifted more than 10%	high
#P015	operational	treatment	guidance	Reverse Osmosis Achievement Turbidity Range	drinking water	treatment_goal	0.010-0.015 NTU	Certain filtration methods, such as reverse osmosis, can achieve turbidity values that approach those of pure water	when using reverse osmosis filtration	high
#P016	design	operational	mandatory	Industry standard nephelometer wavelength (Visible)	drinking water	requirement	400-600 nm	Industry standards require nephelometers to operate in the visible or infrared ranges	Visible range operation	high
#P017	design	operational	mandatory	Industry standard nephelometer wavelength (Infrared)	drinking water	requirement	800-900 nm	Industry standards require nephelometers to operate in the visible or infrared ranges	Infrared range operation	high
#P018	design	operational	mandatory	Design measurement angle for low turbidity	drinking water	requirement	90 degrees	current international standards have determined the most appropriate angle to be 90 degrees for the measurement of low turbidities	generally below 40 NTU	high
#P019	design	operational	mandatory	Turbidimeter Light Path (Standard Methods)	drinking water	requirement	<= 10 cm	Specifications for APHA/AWWA/WEF Standard Method 2130B and U.S. EPA Method 180.1 Rev. 2.0	Applies to these specific recognized methods	high
#P020	design	operational	mandatory	Tungsten lamp color temperature	drinking water	requirement	2200-3000 K	Standard Method 2130B and U.S. EPA Method 180.1 Rev. 2.0 specification	Design for recognized nephelometric methods	high
#P021	operational	operational	guidance	Electronic particle counting range	drinking water	requirement	1-150 µm	Electronic particle counters are now available that are capable of accurately counting and recording the number of particles as a function of size		high
#P022	operational	operational	guidance	Lower size detection limit for particle counters	drinking water	requirement	1-2.5 µm	the lower size for detection by particle counters is in the range of 1-2.5 µm		high
#P023	operational	operational	mandatory	Standard Method 2130B Measurement Range	drinking water	requirement	0 to > 1000 NTU	Applicable measurement range for APHA/AWWA/WEF Standard Method 2130B	Standard design with Tungsten lamp	high
#P024	operational	operational	mandatory	U.S. EPA Method 180.1 Rev. 2.0 Measurement Range	drinking water	requirement	0-40 NTU	Applicable measurement range for U.S. EPA Method 180.1	Standard design with Tungsten lamp	high
#P025	design	operational	mandatory	ISO 7027 Radiation Source Wavelength	drinking water	requirement	860 nm	Radiation source at 860 nm (or 550 nm if sample is colourless)	ISO 7027 design requirements	high
#P026	design	operational	mandatory	ISO 7027 Aperture Angle	drinking water	requirement	20-30 degrees	ISO 7027 design requirement for aperture angle	For radiation source and perpendicular detector	high
#P027	operational	operational	mandatory	ISO 7027 Measurement Range (Diffuse Radiation)	drinking water	requirement	0-40 FNU	Applicable range for diffuse radiation method	ISO 7027	high
#P028	operational	operational	mandatory	ISO 7027 Measurement Range (Attenuation)	drinking water	requirement	40-4000 FAU	Applicable range for attenuation of radiant flux method	ISO 7027	high
#P029	operational	operational	mandatory	GLI Method 2 Measurement Range	drinking water	requirement	0-40 NTU	Applicable measurement range for GLI Method 2	Direct measurement (allows dilution above 40 NTU)	high
#P030	design	operational	mandatory	GLI Method 2 Pulse Frequency	drinking water	requirement	0.5 seconds	Light sources alternately pulse each 0.5 seconds	GLI Method 2 design specification	high
#P031	design	operational	mandatory	Hach Method 10133 Laser Diode Wavelength	drinking water	requirement	660 nm	Laser diode wavelength for Hach FilterTrak Method 10133		high
#P032	operational	operational	mandatory	ASTM D6698-07 Measurement Range	drinking water	requirement	<= 0.02-5.0 NTU	Applicable measurement range for online measurement of turbidity below 5 NTU	ASTM D6698-07	high
#P033	design	operational	mandatory	FNU Instrument Light Source Wavelength	drinking water	requirement	860 ± 60 nm	Instruments that measure turbidity in formazin nephelometric units (FNUs) use a light-emitting diode	Detector at 90 degrees to incident beam	high
#P034	design	operational	mandatory	FAU Instrument Detector Angle	drinking water	requirement	180 degrees	Instruments that measure turbidity in formazin attenuation units (FAUs) use a detector at 180 degrees	Light source at 860 ± 60 nm	high
#P035	operational	operational	guidance	Nephelometer Effective Particle Size Range	drinking water	requirement	0.2-1 µm	Nephelometers are most effective for measuring light scattered by particles in this size range	Peak scatter at approximately 0.2 µm	high
#P036	operational	treatment	guidance	Typical Filtered Water Turbidity Level	drinking water	treatment_goal	< 0.1 NTU	Filtered water turbidity is often below 0.1 NTU	Typical treatment plant performance	high
#P037	operational	operational	guidance	Bubble Interference Turbidity Spike	drinking water	requirement	2.0 NTU	bubbles can cause turbidity spikes as large as 2.0 NTU	Depends on instrument type and gas supersaturation	high
#P038	operational	operational	guidance	Laser Nephelometer Particle Detection Limit	drinking water	requirement	< 0.01 µm	measurement of a submicrometre particle breakthrough event was possible	Using laser nephelometer	high
#P039	operational	operational	mandatory	ASTM D6855-10 Measurement Range	drinking water	requirement	0.02-5.0 NTU or FNU	Applicable measurement range for the static measurement of turbidity below 5 NTU in water	ASTM D6855-10 method	high
#P040	operational	operational	mandatory	Hach FilterTrak Method 10133 Rev. 2.0 Measurement Range	drinking water	requirement	0-5.0 NTU	Applicable measurement range (0-5000 mNTUs)	Hach FilterTrak Method 10133	high
#P041	design	operational	mandatory	Hach FilterTrak Method 10133 Rev. 2.0 Light Path	drinking water	requirement	<= 10 cm	Light path specification for Hach Method 10133	Detector/receiver which may use photomultiplier tube and fibre optic cable	high
#P042	design	operational	mandatory	GLI Method 2 Wavelength	drinking water	requirement	860 nm	Two perpendicular 860 nm light sources alternately pulse	GLI Method 2 design	high

D Definitions (15)

Req ID	Name	Context	Confidence
#D001	EPA	U.S. Environmental Protection Agency	high
#D002	APHA	American Public Health Association	high
#D003	AWWA	American Water Works Association	high
#D004	WEF	Water Environment Federation	high
#D005	ISO	International Organization for Standardization	high
#D006	ASTM	ASTM International	high
#D007	QA/QC	quality assurance and quality control	high
#D008	FAU	formazin attenuation unit	high
#D009	FNU	formazin nephelometric unit	high
#D010	Nephelometry	Nephelometry determines turbidity using the intensity of scattered light measured by a detector that is at 90 degrees to the incident light source.	high
#D011	Ratio technologies	technologies which are based on the use of a 90 degree detector in combination with another detector set at a different angle that determine the turbidity of a sample	high
#D012	Electronic particle counters	instruments that are capable of accurately counting and recording the number of particles as a function of size (often in the 1-150 µm range)	high
#D013	mNTU	0.001 NTU	high
#D014	FNU	formazin nephelometric unit; instruments that measure turbidity in these units use a light-emitting diode with a wavelength of 860 ± 60 nm as a light source and a detector at 90 degrees to the incident light beam	high
#D015	FAU	formazin attenuation unit; instruments that measure turbidity in these units use a light-emitting diode with a wavelength of 860 ± 60 nm and a detector at 180 degrees to the incident light beam	high