Turbidity meter

Apera’s TN500 is the turbidity meter I’d carry for drinking water, and I’ve used it. Apera says it uses a tungsten filament lamp and the 90 degree scattering method, fully compliant with U.S. EPA 180.1, for tap water, drinking water, wastewater and environmental samples.

It reads 0 to 1,000 NTU with automatic ranges: 0.01 to 19.99, 20.0 to 99.9, and 100 to 1,000 NTU. Accuracy is ±2 percent of reading plus stray light, repeatability is ±1 percent or 0.02 NTU, whichever is greater, and stray light is 0.02 NTU or less.

Apera says the tungsten lamp is especially good for low-range water under 10 NTU, and that the lamp is user-replaceable.

The kit includes AMCO polymer standards at 0, 20, 100, 400 and 800 NTU. Apera calls them EPA-approved, NIST-traceable and non-toxic, with a guaranteed one-year shelf life, and says to store them at room temperature and never let them freeze.

Its TruRead mode takes several readings in a row and shows the average, minimum and maximum, which helps with samples that settle. It has zero-point calibration with an error reminder.

The TN500 stores 200 sets of readings with a real-time clock and calibration history, and exports them over USB with Apera’s PC-Link software. The rechargeable 3.7 V lithium battery runs up to 20 hours.

The housing is IP67, the vials are 25 by 60 mm borosilicate glass holding 18 mL, and Apera lists a 2-year limited warranty. It scored 10 on every check.

The kit includes the meter, the five standards, six sample vials, silicone oil, a microfiber wipe, a USB charger and cable, the PC-Link software on a flash drive and a carrying case. The color screen shows guides in English, Spanish and Chinese, and the meter powers itself off when idle.

My call: oil the vial with the silicone oil in the kit and wipe it with the cloth every time. EPA Method 180.1 says sample tubes must be kept clean inside and out and never handled where the light strikes them.

LaMotte’s 2020t is the turbidity meter I’d pick when I want ratio readings, and I’ve used it. LaMotte says the 2020t meets the U.S. EPA design criteria in EPA 180.1, Rev. 2.0 (1993), and Standard Methods 2130 B-2001.

Its design is ratiometric. LaMotte says the multi-detector optics assure long-term stability and minimize stray light and color interference, and the meter can read in ratio (NTRU), plain nephelometric (NTU) or attenuation units.

In ratio mode it reads 0 to 1,000 NTRU. Resolution is 0.01 up to 10.99, 0.1 up to 109.9 and 1 above that, and the detection limit is 0.05.

LaMotte lists accuracy as ±0.05 from 0 to 2.5 NTRU, ±2 percent from 2.5 to 100, and ±3 percent from 100 to 1,000, and calls the meter ideally suited for low-level drinking water applications.

The kit comes with 0, 1 and 10 NTU standards, a sample bottle, six sample tubes, a USB cable and a wall adapter in a carrying case. Stored results can be viewed on the meter, and it has a backlit display; LaMotte’s page lists seven user-selected languages in one place and eight in another.

It’s waterproof to IP67 and runs on a rechargeable lithium-ion battery.

It also reads the brewing units ASBC and EBC: up to 17,500 ASBC and 250 EBC in ratio mode, per LaMotte, which makes it useful beyond plumbing for anyone checking beer or wort clarity.

Below 11 NTU it resolves 0.01, and its detection limit of 0.05 NTU is the figure to look at when you’re checking finished drinking water.

Where it lost points: ±3 percent above 100 NTU scored 9, and three standards instead of five scored 8. The infrared version, the 2020i, follows ISO 7027 and ships with 0, 10 and 100 FNU standards.

My call: for clear, treated water, the 1 and 10 NTU standards are the ones that matter. Calibrate close to the range you actually test.

Apera’s TN480 is the turbidity meter I’d hand someone testing colored water, and I’ve used it. Apera says it uses an infrared light source and the 90 degree scattering method, compliant with ISO 7027, and calls infrared especially ideal for samples with color.

EPA’s own method explains why color matters. Method 180.1 says true color, from dissolved substances that absorb light, makes a white-light turbidity reading low, though it adds the effect is generally not significant in drinking water.

It reads 0 to 1,000 NTU (FNU) with automatic ranges, the same as the TN500. Accuracy is ±2 percent of reading plus stray light, repeatability is ±1 percent or 0.02 NTU, whichever is greater, and stray light is 0.02 NTU or less.

The kit has AMCO polymer standards at 0, 20, 100, 400 and 800 NTU, six sample vials, a USB cable, silicone oil, a microfiber wipe, Apera’s PC-Link software on a flash drive and the manual, all in a rugged carrying case.

It stores 200 sets of readings with a real-time clock and a calibration date check, and sends them over USB to a Windows PC. It also powers itself off and warns when the batteries run low.

Its TruRead mode takes several readings in a row and reports them, which helps with samples that settle. The detector is a silicon photovoltaic cell, per Apera.

It runs on four AA alkaline batteries. The housing is IP67, it works from 32 to 122°F, the meter measures 90 by 203 by 80 mm and weighs 385 grams, and Apera lists a 2-year limited warranty from delivery.

Where it lost points: AA batteries instead of a rechargeable pack scored 7. Every other check scored 10, which ties it with the LaMotte.

Apera’s TN400 is the same infrared meter without the log and without TruRead; it’s in the left-out table with its score.

My call: keep a spare set of AA batteries in the case, and check the calibration date on screen before a day of testing.