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This guide covers the medical water trap used with breathing tubes. Plumbing P-traps and other non-medical “water traps” are different devices and are not covered. General product information only, not medical advice.
Short answer
A water trap is a small device that collects and drains the water that condenses in breathing tubing. FDA’s regulation calls it a “tee drain (water trap)”: a device intended to trap and drain water that collects in ventilator tubing during respiratory therapy, thereby preventing an increase in breathing resistance. It is a Class I device under 21 CFR 868.5995.
What is a water trap? Definition and scope
Under 21 CFR 868.5995, a tee drain (water trap) is classified as Class I (general controls) and is exempt from premarket notification, subject to the limitations in 21 CFR 868.9. FDA’s product classification database lists it under product code BYH, “Drain, tee (water trap)”, in the anesthesiology medical specialty, reviewed by the Division of Anesthesia, Respiratory, and Sleep Devices. Establishments making exempt Class I devices must still register with FDA.
The same name is used in practice for two product families that differ in the circuit they sit in, whether they are reusable, and how long they stay in service. The table below compares them using each manufacturer’s own instructions for use (IFU).
How a water trap is used in practice
Warm, humidified gas cools as it travels through tubing, and the water that condenses has to go somewhere. The regulation’s stated purpose is to trap and drain that water so that it does not raise breathing resistance. Two examples from the manufacturer IFUs below show the intended use of each product type:
- Fisher and Paykel Healthcare’s autoclavable water trap (900MR139) is intended to collect condensate from expiratory breathing tubes of its reusable breathing circuits.
- The Airlife inline water trap is intended to collect excess condensation that may have collected in oxygen tubing, placed between the cannula tubing and the supplemental oxygen tubing. It is for spontaneously breathing infant, pediatric and adult users.
Clinical set-up and handling instructions belong in the product’s IFU and local protocols, not in a general guide.
Ventilator-circuit trap vs inline oxygen-tubing trap
| Item | Reusable ventilator-circuit trap (Fisher and Paykel 900MR139) | Inline oxygen-tubing trap (Airlife, 840097) |
|---|---|---|
| Intended use | Collect condensate from expiratory breathing tubes of reusable breathing circuits | Collect excess condensation in oxygen tubing |
| Where used | Hospital or clinical environments; to be prescribed by a physician | Hospitals, sub-acute, clinics, pre-hospital, home, surgical centers, skilled nursing |
| Reuse | Reprocessable per the manufacturer’s reprocessing instructions (UI-623716); incorrect reprocessing risks cross-infection | Non-sterile, disposable, single-patient use; not intended to be cleaned or reused |
| Service limit | Discard after 50 reprocessing cycles, or five years from date of manufacture | Discard and replace at 3 months, or sooner if soiled, discolored or cracked |
| Condition limits | Discard if cracked, torn or damaged | Discard if soiled, discolored or cracked |
Source for the table: the two manufacturer IFUs listed under Sources, checked 2026-10-30.
Where it matters for clinics and supply decisions
The IFU lines above translate into a short checklist of things the manufacturer says to confirm for a given product. It is a reading aid, not purchasing advice.
- Single-patient or reusable. The Airlife IFU says disposable and single-patient; the Fisher and Paykel IFU says reprocess and gives a cycle limit.
- Reprocessing instructions. For the reusable trap, the IFU points to a separate reprocessing document (UI-623716) and warns of cross-infection if reprocessing is incorrect.
- Discard limits. 50 reprocessing cycles or five years (reusable); 3 months (inline oxygen-tubing).
- Circuit compatibility. The reusable trap has a stated maximum operating pressure of 80 hPa (cmH2O), and its IFU warns that components not compliant with ISO 5367 / ISO 80601-2-74 may cause disconnection, and says not to modify the device or lubricate connections.
- Environment limits. The reusable trap is not for flammable anesthetic gas mixtures or Heliox, and not for use during X-ray, MRI or RF procedures.
- Regulatory identity. The tee-drain classification (Class I, product code BYH) applies to the device type; the specific product’s labeling and IFU still govern its use.
Common misunderstandings
- “Water trap” means plumbing. In plumbing the term refers to a P-trap or S-bend; this guide is about the respiratory-care device only.
- All medical water traps are interchangeable. The two IFUs above differ on reuse, discard limits, circuit type and intended population, so one product’s rules do not carry over to another.
- A water trap lasts indefinitely. The inline oxygen-tubing IFU sets a 3-month discard; the reusable trap’s IFU sets cycle and age limits and says to discard it if damaged.
- It does the job of other tubing accessories. The regulation describes water collection and drainage only. For related devices, see the guides on HME filters for tracheostomy and the oxygen concentrator humidifier.
For oxygen delivery tubing generally, see the oxygen tubing guide; for sleep-therapy circuits, CPAP accessories and what a CPAP machine is.
FAQ
What is a water trap?
In respiratory care, a water trap (FDA name: tee drain) is a device that collects and drains condensed water from breathing tubing so it does not increase breathing resistance. FDA classifies it as Class I under 21 CFR 868.5995, product code BYH, exempt from 510(k) premarket notification subject to 21 CFR 868.9.
What is a water trap in a ventilator circuit?
It is the collection point for condensate in the tubing. One manufacturer’s IFU describes its reusable trap as intended to collect condensate from the expiratory breathing tubes of its reusable breathing circuits.
Is a water trap reusable?
It depends on the product. The Fisher and Paykel 900MR139 is reprocessable up to 50 cycles or five years; the Airlife inline oxygen-tubing trap is disposable, single-patient and replaced at 3 months.
Sources
Primary sources checked 2026-10-30.
- eCFR, 21 CFR 868.5995 Tee drain (water trap), https://www.ecfr.gov/current/title-21/chapter-I/subchapter-H/part-868/subpart-F/section-868.5995 (checked 2026-10-30).
- FDA Product Classification, code BYH, https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpcd/classification.cfm?id=BYH (checked 2026-10-30).
- Fisher and Paykel Healthcare, Autoclavable watertrap 900MR139 user instructions (UI-623684), https://resources.fphcare.com/content/900mr139-autoclavable-watertrap-ui-623684.pdf (checked 2026-10-30).
- Airlife (Vyaire), Inline Water Trap instructions 840097 Rev B, https://connect.myairlife.com/resources/840097_WaterTrap_RevB.pdf (checked 2026-10-30).
