A turbidimeter's job is simple to state and easy to get wrong in practice: match the NTU range and measurement method to your application, then keep the instrument in calibration. This guide covers how nephelometric turbidity measurement works, which NTU range and meter type fit drinking water, wastewater, and environmental sampling work, and a field-ready calibration protocol.
What Does a Turbidimeter Actually Measure?
A turbidimeter measures how much light scatters when it passes through a water sample — the more suspended particles (silt, clay, algae, organic matter, floc), the more the light scatters, and the higher the reading in Nephelometric Turbidity Units (NTU). It is a proxy for suspended solids and filtration performance, not a direct contaminant measurement.
Turbidity readings drive decisions in several Canadian environmental and industrial contexts: verifying filter performance at a drinking water treatment plant, confirming treated effluent meets discharge limits before release, monitoring stormwater runoff at construction and industrial sites, and assessing groundwater sample clarity during well development for Phase II ESA work (see our Phase II ESA equipment checklist). Health Canada's Guidelines for Canadian Drinking Water Quality treat turbidity as a treatment-technique parameter rather than a single numeric limit — the goal is consistently low, stable readings that confirm filtration and disinfection are working, not just a pass/fail number.
Why Turbidity Matters Beyond Aesthetics
High turbidity does more than cloud the water. Suspended particles shield pathogens from disinfection (chlorine and UV both lose effectiveness in turbid water), clog membranes and filter media prematurely, and — in receiving waters — smother fish habitat and block light for aquatic vegetation. That is why turbidity appears in Canadian drinking water guidelines, provincial effluent permits, and stormwater management plans as a routine compliance parameter, not an optional check.
What NTU Range Do You Need for Your Application?
Match the meter's range to the water you actually test — a low-range drinking water instrument wastes its resolution on a wastewater sample, and a high-range unit loses precision on near-zero treated water.
| Application | Typical NTU Range | Recommended Instrument |
|---|---|---|
| Treated drinking water / filter performance | 0–10 NTU (target <1 NTU) | HI98703-01 — EPA-compliant portable turbidimeter |
| Water treatment plant + disinfection monitoring | 0–10 NTU turbidity, 0–5 mg/L chlorine | HI93414 — combined turbidity/chlorine photometer |
| Wastewater, process water, industrial effluent | 10–1,000 NTU | HI98703-01 or HI93414 (ratio mode) |
| High-turbidity industrial samples, sludge supernatant | Up to 4,000 NTU (ratio mode) | HI83414 / HI88703 benchtop meters |
| Continuous multiparameter field profiling (turbidity + pH/DO/EC) | 0–1,000 FNU | HI9829 submersible probe |
Note the unit change in the last row — the HI9829 reports turbidity in FNU (Formazin Nephelometric Units) from its submersible probe, not NTU. See the FAQ below on why that distinction matters when comparing spec sheets across instrument types.
Nephelometric vs. Ratio Turbidimeters: What's the Difference?
A standard nephelometric turbidimeter detects scattered light at a single 90° angle from the incident beam. A ratio turbidimeter adds a second detector at 180° and calculates a ratio between the two readings — which corrects for colour and light-absorbing compounds in the sample and extends the usable range well beyond what single-angle detection can measure accurately.
ERE's Hanna Instruments turbidimeters use ratio nephelometric measurement — an adaptation of USEPA Method 180.1 and Standard Method 2130 B — with automatic range selection between 0.00–9.99, 10.0–99.9, and 100–1,000 (or up to 4,000 on the benchtop HI83414) NTU. The tungsten filament light source and silicon photocell detector combination is standard across the line, with accuracy of ±2% of reading plus 0.02 NTU on the portable models.
Non-Ratio Mode: When a Single Angle Is Enough
The benchtop HI83414/HI88703 also offers a non-ratio mode (0.00–40.0 NTU) for clean-water applications where the extended range and interference correction of ratio mode aren't needed — non-ratio measurement is faster and adequate for routine drinking water screening.
Does Your Application Require EPA-Compliant Measurement?
If you're reporting turbidity for regulatory compliance — drinking water treatment records, effluent monitoring under a provincial discharge permit, or documentation for an environmental consultant's report — use an instrument built to USEPA Method 180.1 / Standard Method 2130 B with NIST-traceable calibration standards and a documented Cal Check verification. The HI98703-01 and HI93414 are built for exactly this: EPA-compliant tungsten light source, ratio nephelometric method, USB/RS232 data logging with time-and-location tagging for up to 200 records, and Cal Check calibration verification against certified standards.
For field screening where you need a fast go/no-go read — checking stormwater discharge clarity during a rain event, or a quick well-development check before deploying lab-grade sampling equipment — the accuracy bar is lower and a portable unit with basic calibration is sufficient. The distinction matters for how you document your results, not just which button you press.
How to Calibrate a Turbidimeter: A 5-Step Field Protocol
Calibrate before each field day for compliance work, and verify against a check standard between full calibrations. The protocol below applies to any Hanna ratio turbidimeter.
- Select NIST-traceable standards that bracket your expected range. ERE stocks AMCO-AEPA-1 calibration solutions at <0.1, 20, 100/500, and higher NTU/FTU values — a stabilized styrene-divinylbenzene copolymer suspension that replaces liquid formazin as the EPA-recognized primary standard.
- Inspect and clean the sample cuvettes. Scratches, fingerprints, and water spots scatter light independently of the sample and will bias every reading taken with that cuvette.
- Apply a thin film of silicone oil to the cuvette exterior and wipe evenly. This fills micro-scratches on the glass and equalizes the optical path — skipping this step is one of the most common sources of drift complaints in the field.
- Run a multi-point calibration. The HI98703-01 and HI93414 support 2-, 3-, or 4-point calibration; the benchtop HI83414/HI88703 support 2- to 5-point calibration. Use at least 3 points across your working range for compliance-grade results.
- Verify with an independent Cal Check standard before recording field data. If the verification reading drifts outside tolerance, recalibrate — don't average it out. Recalibrate immediately after any lamp or battery replacement, and on a fixed schedule (typically monthly for active field use) even if verification passes.
ERE's instrument repair and calibration service handles annual certified calibration and lamp replacement for Hanna turbidimeters if you'd rather not carry standards and cuvette-prep supplies to every site.
Turbidimeter or Multiparameter Probe: Which Should You Buy?
Buy a dedicated turbidimeter when turbidity is the parameter you report on and precision matters — the HI98703-01's 0.01 NTU resolution at the low end and EPA-adapted method beat what any multiparameter probe delivers for that single parameter. Buy the HI9829 multiparameter meter when you need turbidity alongside pH, ORP, dissolved oxygen, and conductivity from one submersible IP68 probe in a single field visit — common on groundwater monitoring rounds and surface water profiling where minimizing equipment and site time matters more than the last decimal point of turbidity resolution. See our water quality meters buyer's guide for the full multiparameter-vs-single-parameter comparison, and our Solinst Levelogger guide if continuous groundwater-level logging is also part of your monitoring program.
Browse ERE's full water quality instrumentation collection for the complete Hanna Instruments turbidity and multiparameter lineup.
Need help specifying a turbidimeter for your site?
ERE Inc. has been Canada's environmental and industrial instrumentation specialist for 30+ years. Tell us your NTU range, sample type, and reporting requirements, and we'll recommend the right Hanna Instruments model — not the most expensive one.
→ Request a Quote | 1-888-287-EREC | Browse Water Quality Instruments | sales@ereinc.com
Frequently Asked Questions
What turbidity level is acceptable for treated drinking water in Canada?
Health Canada's drinking water guidance treats turbidity as a treatment-technique parameter tied to filtration performance rather than a single hard limit: the widely applied industry benchmark is turbidity at or below 0.3 NTU in at least 95% of filtered water samples, never exceeding 1 NTU. Provincial drinking water regulations set the enforceable requirements for your specific system — confirm the applicable limit with your provincial regulator or engineer of record.
Can one turbidimeter cover both drinking water and wastewater monitoring?
Yes, if it supports ratio mode. The HI98703-01 and HI93414 auto-range from 0.00 NTU up to 1,000 NTU in ratio mode, covering treated water through most process and wastewater samples. For samples routinely above 1,000 NTU — settled sludge, raw influent, some industrial effluents — the benchtop HI83414/HI88703 extends to 4,000 NTU.
How often should a turbidimeter be calibrated?
Full multi-point calibration before each compliance-monitoring field day is standard practice, with Cal Check verification against an independent standard between full calibrations. For continuous benchtop use, weekly full calibration with daily verification is typical. Always recalibrate after replacing the lamp or battery.
What's the difference between NTU, FNU, and FTU?
NTU (Nephelometric Turbidity Unit) is the USEPA Method 180.1 unit used by the HI98703-01, HI93414, and HI83414/HI88703. FNU (Formazin Nephelometric Unit) is the ISO 7027 unit used by submersible probes like the HI9829. FTU (Formazin Turbidity Unit) appears on some non-ratio readings. The three track closely using formazin-based standards but are not interchangeable specification-to-specification — compare instruments within the same unit system, or confirm the conversion basis with ERE before comparing spec sheets across brands.
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Lire en français : Guide de sélection d'un turbidimètre pour la surveillance environnementale au Canada