Tool
Water checker: is my water safe for carnivorous plants?
Carnivorous plants are killed by dissolved minerals that ordinary houseplants shrug off. Enter a meter reading and the checker compares it with the limits published by the International Carnivorous Plant Society [1, 2].
The limits the checker uses
| Water for | Use it when TDS is below | What the source says |
|---|---|---|
| Established plants in pots (flytraps, sundews, pitcher plants) | 90 ppm | The ICPS Venus flytrap guide says tap water with a TDS below 90 ppm can be used; above that, use distilled, reverse osmosis or clean rain water.[1] |
| Seeds and seedlings | 80 ppm | The ICPS seed germination guide asks for water with less than 80 ppm of dissolved solids.[2] |
| Sarracenia outdoors that also get plenty of rain | 100 ppm | The ICPS page on displaying Sarracenia outdoors says tap water under 100 ppm TDS, or plenty of summer rain you can collect, puts you in good shape.[3] |
Converting an EC reading
Conductivity meters estimate dissolved solids by multiplying EC by a conversion factor, and the factor rises with conductivity. The checker interpolates between the factors NDSU Extension publishes for natural waters[5]:
| EC (µS/cm) | Factor | Approximate TDS (ppm) |
|---|---|---|
| 100 | 0.50 | 50 |
| 500 | 0.60 | 300 |
| 1,000 | 0.65 | 650 |
| 1,500 | 0.70 | 1,050 |
| 2,000 | 0.72 | 1,440 |
| 2,500 | 0.74 | 1,850 |
How the checker decides
The checker compares your reading with one fixed number, and which number depends on what the water is for. The International Carnivorous Plant Society (ICPS) does not publish a single universal limit; its pages give slightly different figures for different situations, and the checker keeps them apart rather than averaging them:
- Established potted plants: the ICPS Venus flytrap guide says tap water with total dissolved solids (TDS) below 90 ppm can be used, and that water above 90 ppm should be replaced with distilled, reverse osmosis or clean rain water [1].
- Seeds and seedlings: the ICPS seed germination guide asks for water with less than 80 ppm of dissolved solids [2].
- Sarracenia growing outdoors: the ICPS page on displaying Sarracenia outdoors says that water under 100 ppm, or plenty of summer rain you can collect, puts you in good shape [3]. Rain flushes the pots, which is why this figure is a little more generous.
A reading exactly at the limit counts as over it, because each source phrases its figure as “less than”.
Reading TDS or EC
A TDS meter reports parts per million (ppm), which is the same as milligrams per litre [5]. Conductivity (EC) meters report microsiemens per centimetre; the meter, or this checker, turns that into an estimated TDS by multiplying by a conversion factor. NDSU Extension publishes factors for natural waters that rise from about 0.50 at 100 µS/cm to 0.65 at 1,000 µS/cm, and the checker interpolates between them [5]. Below 100 µS/cm it uses 0.50, the lowest factor in that table, so treat very low EC estimates as approximate.
When a reading lands within about 10 ppm of the limit, the checker says so. Meters drift, and NDSU advises checking an EC meter against a calibration solution regularly [5].
What the checker cannot tell you
TDS measures the total amount of dissolved material, not which minerals are present. A passing reading does not cover fertilizer or lime mixed into the soil, salty perlite, or salts that build up in a pot over time; the ICPS soil page warns about all three [6]. Water quality can also change with the season or the supply. For scale, the ICPS rhizome rot page shows Sarracenia that died after being watered with water at TDS 350 and pH 8 and allowed to dry out [4].
If your reading is over the limit, the water guide explains the alternatives, and mineral burn describes what damage from hard water looks like.
Sources
- Growing Dionaea muscipula. International Carnivorous Plant Society. TDS under 90 ppm; dormancy only for plants facing freezing weather outdoors; LED wattage and lux; USDA-zone advice; soil choices. Accessed October 12, 2026.
- Seed Germination Guide. International Carnivorous Plant Society. Water for seeds under 80 ppm dissolved solids. Accessed October 12, 2026.
- Display Sarracenia on your deck. International Carnivorous Plant Society. Tap water under 100 ppm TDS, or plenty of rain, for outdoor Sarracenia. Accessed October 12, 2026.
- Sarracenia Rhizome Rot. International Carnivorous Plant Society. Plants killed by salty water (TDS 350, pH 8) combined with drying out. Accessed October 12, 2026.
- Using Electrical Conductivity and Total Dissolved Solids Meters to Field Test Water Quality (WQ1923). North Dakota State University Extension. EC-to-TDS conversion factors for natural waters; meters need regular calibration. Accessed October 12, 2026.
- Peat, Sand, Perlite. International Carnivorous Plant Society. Equal peat and coarse sand as the default mix; sand grain 1.5 to 2 mm; perlite caveats. Accessed October 12, 2026.