FreshWater Watch archive
The FreshWater Watch test kit: what is in it and how a reading is taken
This address: freshwaterwatch.thewaterhub.org once held FreshWater Watch's guide to its volunteer test kit. Earthwatch runs the programme at freshwaterwatch.org and supplies kits to its groups; this page is The Water Hub's own description, from the programme's methods manual and the studies that tested the kit.
The FreshWater Watch kit is a set of colour-change tests a volunteer uses at the water's edge: one tube for nitrate, one for phosphate, a clear tube for turbidity, a sample cup and colour cards (the methods manual). Each tube draws up a fixed amount of water, changes colour in three to five minutes, and is read against a colour card as one of seven concentration bands.
What is in the kit
The starter kit holds an instruction sheet, a Secchi tube, a sample cup, nitrate and phosphate colour cards and the nitrate and phosphate tests themselves (the methods manual). The tests are Kyoritsu PackTests from Japan, each drawing a standard 1.5 mL of water and reading it as one of seven discrete ranges (Bishop and others, 2020). Kyoritsu's nitrate tube uses a reduction and naphthylethylenediamine colour method and reads in three minutes; the phosphate tube's enzyme method reads in five (Kyoritsu, archived).
The bands the colour cards read
A reading is recorded as the band between the two closest colour matches on the card, nitrate as nitrogen and phosphate as phosphorus (Hegarty and others, 2021, table 1). To convert the kit's nitrate figure to nitrate as NO3, multiply by 4.4: the top band, over 10 mg/L, is over 44 mg/L as NO3 (FreshWater Watch FAQ).
| Band | Nitrate (as N) | Phosphate (as P) |
|---|---|---|
| 1 | under 0.2 | under 0.02 |
| 2 | 0.2 to 0.5 | 0.02 to 0.05 |
| 3 | 0.5 to 1 | 0.05 to 0.1 |
| 4 | 1 to 2 | 0.1 to 0.2 |
| 5 | 2 to 5 | 0.2 to 0.5 |
| 6 | 5 to 10 | 0.5 to 1 |
| 7 | over 10 | over 1 |
Taking a reading, step by step
Rinse the sample cup twice in the water and fill it to the line. Pull the small yellow pin from the tube, squeeze its sides to push out about half the air, dip the open end into the cup and let go, so the tube draws the sample in, then shake it. Wait three minutes for nitrate or five for phosphate, and match the colour against the card out of direct sunlight (the methods manual). Below 10°C the reaction slows, so hold the tubes in your hand: at 10°C phosphate can take 20 minutes rather than five (Freshwater Habitats Trust, quoting Kyoritsu). The tests are calibrated for fresh water only, below 1 ppt salinity (FreshWater Watch FAQ).
The turbidity tube
Clarity is read with a clear plastic tube 50 mm wide, marked on a non-linear scale of nephelometric turbidity units calibrated with formazin (Bishop and others, 2025; the manual gives its length as 0.5 m and the paper as 0.45 m). Water is poured in until the disc at the bottom disappears and the reading is the mark above: if it disappears between the 100 and 75 NTU marks, record 100 NTU (the methods manual).
How accurate the kit is
Against a laboratory photometer, sixteen paired readings agreed well for phosphate and less well for nitrate (Spearman's rho 0.93 and 0.76), with phosphate tending to read low (Bishop and others, 2025). On Lake Tanganyika the kit's overall accuracy against laboratory analysis was 91% for nitrate and 74% for phosphate (Moshi and others, 2022), and a Freshwater Habitats Trust trial found that a tube showing no colour change was very likely clean water: 98% of the time for phosphorus and 81% for nitrate.
Testing your own drinking water
The same nitrate test matters at home. The US limit for nitrate in public drinking water is 10 mg/L as nitrogen (EPA), the figure where the kit's top band starts. EPA advises testing a private well every year for total coliform bacteria and nitrates, and using a laboratory certified for drinking water testing (EPA, private wells); our answer on home water test kits compares what a household can buy.
Next: water testing services compared on The Water Hub.
Questions
What is in the FreshWater Watch test kit?
Kyoritsu colour-change tubes for nitrate and phosphate, colour cards, a sample cup, a Secchi turbidity tube and an instruction sheet.
How long does a FreshWater Watch reading take?
Three minutes for nitrate and five for phosphate at normal temperatures; below 10°C hold the tubes in your hand, as phosphate can take 20 minutes.
How accurate are the FreshWater Watch tests?
In published comparisons with laboratories, accuracy was 91% for nitrate and 74% for phosphate on Lake Tanganyika, and readings correlated at 0.76 and 0.93 with a photometer.
Can I use the kit to test drinking water?
It shows nitrate bands up to over 10 mg/L as nitrogen, the US drinking water limit, but EPA advises a certified laboratory for a well's annual test.
Sources
- FreshWater Watch methods manual (archived 2022), read 2026-10-21
- Bishop and others, Sustainability, 2020, read 2026-10-21
- Kyoritsu: nitrate PackTest WAK-NO3 (archived 2021), read 2026-10-21
- Kyoritsu: phosphate PackTest WAK-PO4(D) (archived 2021), read 2026-10-21
- Hegarty and others, Science of the Total Environment, 2021, read 2026-10-21
- FreshWater Watch: FAQs, read 2026-10-21
- Freshwater Habitats Trust: Clean Water for Wildlife technical manual, read 2026-10-21
- Bishop and others, Citizen Science: Theory and Practice, 2025, read 2026-10-21
- Moshi and others, Environmental Monitoring and Assessment, 2022, read 2026-10-21
- EPA: National Primary Drinking Water Regulations, read 2026-10-21
- EPA: protect your home's water, read 2026-10-21