Water Purity for Carnivorous Plants: TDS Limits and Practical Solutions

A grower with well water showing visible mineral deposits asked how pure water must be for carnivorous plants, noting that some genera tolerate more minerals than others.

What Matters: Dissolved Minerals, Not Toxins

Jeff Dallas explains: Heavy metals (lead, mercury) don't harm carnivorous plants much, but calcium and magnesium (hardness) are deadly over time. Total Dissolved Solids (TDS) in parts per million (ppm) is the standard measure.

• ≤50 ppm: Safe for most CPs long-term.
• Example: Portland tap water at 20 ppm worked for years; a well at 130 ppm killed flytraps in one year.

Genus Tolerance Ranking

• Most sensitive: Venus flytraps, sundews.
• Moderate: Sarracenia (tolerates harder water longer, especially outdoors where rain flushes minerals).
• Least sensitive: Nepenthes (can handle higher TDS).

Practical Advice

• Test your water (aquarium stores often offer free TDS testing).
• Use rain, distilled, or RO water for sensitive species.
• Well water is acceptable for Nepenthes and outdoor Sarracenia.
• Carbon filters (Brita, Pur) remove chlorine and some metals but not calcium/magnesium.
• Live sphagnum moss as top dressing does not remove minerals; hard water will kill the moss.

The grower, located in Coos County, Oregon, was encouraged to collect abundant rainwater and send a sample for free testing if desired.