Hemp Thread Sealing and Drinking Water: Approved in Germany, Banned in the UK

The same fibre in the same joint is approved drinking-water plumbing in Munich and a code violation in Manchester. The divergence is regulatory, not physical — nobody disputes that a flax-and-paste joint holds water. ## Germany and much of the EU: approved as a certified system German practice treats the fibre and the paste as a single certifiable unit. A jointing paste tested to **DIN EN 751-2** (non-hardening compounds for threaded joints) and carrying a **DVGW** registration, together with KTW migration testing for materials contacting drinking water, is approved for potable water and for domestic gas. Neo-Fermit, a common example, carries a DVGW registration and is rated to about 16 bar at 0–95 °C on drinking water, 7 bar to 130 °C on heating, and 5 bar to 70 °C on gas. German technical writing is explicit that the paste is what makes it legal: for drinking-water installations an approved sealing compound must be used. Bare hemp with an uncertified paste is not the approved article; hemp plus the certified compound is. ## United Kingdom: excluded by the positive list The **Water Supply (Water Fittings) Regulations 1999** work from Schedule 2, a positive list of what may contact drinking water, policed through WRAS approval. Hemp is not on it, which makes it effectively prohibited on potable systems — mains cold and the hot supply derived from it. UK potable practice is a WRAS-approved compound, PTFE tape, or wound cord. Hemp survives in UK trade use on heating circuits and other non-potable work. ## United States: never part of the tradition US potable work runs on **NSF/ANSI 61** listed materials: PTFE tape and NSF-61 pipe dope or anaerobic sealant. Fibre thread sealing was never mainstream in American plumbing, so there was little to prohibit. ## Why two regimes reach opposite answers The mechanism is the difference between **approval by certification** and **precaution by exclusion**. Germany certified the system: test a specific paste, confirm it encapsulates the fibre and does not leach, and list the combination. The UK and US operate positive lists, where a material is legal only once a specific product has passed migration, taste, odour and microbial-growth testing and been listed by name. Loose natural fibre is a poor fit for that structure — it is not a standardised, branded, batch-controlled product that a manufacturer can submit and defend. The general worry behind such lists is that organic material in contact with water can act as a nutrient source supporting biofilm growth in warm, stagnant sections. See Biofilms: The Bacterial Communities 1000× More Resistant to Antibiotics. **An important caveat:** no regulatory document has been found naming a specific contamination incident, or Legionella in particular, as the reason hemp is absent from the UK list. The nutrient rationale is the standard logic of positive-list regimes, not a documented cause of a delisting. The honest formulation is that hemp fails to clear the regime's structure rather than that it was banned for a proven failure. The practical rule for anyone crossing a border with their habits: the fibre is not the variable — the local approval regime is.