👃 Odour and Flavour of Water

Physicochemistry PN-EN 1622

Overview

STATUS (as of 28.10.2026). PN-EN 1622:2006 — English version, published 18.09.2006, implements EN 1622:2006 [IDT]; it replaced PN-EN 1622:2003 (Polish version). The standard is current — no withdrawal note.

SCOPE (clause 1). The standard gives quantitative methods for determining the threshold odour number (TON) and threshold flavour number (TFN), and a qualitative method for detecting abnormal odour or flavour. There are two quantitative methods: a short method — when the sample has no odour or flavour, or when they are compared with a specified threshold number — and a full method, when the threshold number of the sample has to be determined. Both exist in two variants: unforced choice (the main text of the standard, the variant widely used in Europe) and forced choice (Annex B). The methods apply to drinking water and to migration waters from tests of materials in contact with water; the choice of method depends on national regulations and the type of water (raw, distribution, migration).

TERMS (clause 3). TON and TFN are the dilution ratio beyond which the diluted sample has no perceptible odour (TON) or flavour (TFN): TON = TFN = (A + B) / A, where A — volume of sample, B — volume of reference water. Reference water is water described by the panel of assessors as having no perceptible odour and flavour. In the triangle test an assessor receives three vessels: two with reference water and one with the sample or its dilution (or the other way round); in the paired test — two vessels, the sample and reference water. With unforced choice the assessor records whether or not they notice a difference; with forced choice they must choose a vessel even if they perceive no difference.

TEMPERATURE. The standard is primarily intended for assessment at 23 °C: the room is kept at (23 ± 2) °C and the samples are brought to this temperature in a water bath or incubator. Assessment at another temperature is possible, but results obtained at different temperatures cannot be compared.

PANEL OF ASSESSORS (clause 9). At least three selected assessors for unforced choice and eight for forced choice; the simplified qualitative method (Annex C) may be performed by a single assessor. New assessors are introduced by an experienced assessor, and persons with allergy or unusual sensitivity are excluded. The performance of assessors and of the panel has to be monitored, e.g. by interlaboratory tests; the precision of the result depends on the panel size. The standard considers at least 5 persons desirable for the paired test and 6 for the triangle test, but allows a smaller panel with unforced choice if the responses are homogeneous.

ROOM (clause 6). Free from draughts and noise, away from activities that generate odours, no air fresheners, preferably used only for these assessments; assessors must not influence each other. Design guidance — ISO 8589.

DRINKING WATER — LEGAL REQUIREMENT. Regulation of the Minister of Health of 22 May 2026 (Journal of Laws 2026, item 748), Annex 1 Part C: flavour and odour — "acceptable to consumers and no abnormal change". The regulation gives no numerical value of TON or TFN.

WHAT WE DO NOT GIVE HERE. The course of the short and full methods (10.3), the preparation of successive dilutions (Annex F), the criteria for homogeneity of the panel's responses, the table of threshold numbers (Table 1) and the rules for expressing the result (clause 11), the dechlorination procedure (Annex A) or the qualitative method (Annex C) — we only know the titles of these clauses. Therefore we do not give the number of dilutions, vessel volumes, reagent doses or an intensity scale here.

Method principle

The odour and flavour of a sample are assessed quantitatively by a panel of selected assessors who compare the sample or its dilutions with a reference water — water without perceptible odour and flavour. The threshold number is the dilution ratio (A + B) / A beyond which the diluted sample no longer has a perceptible odour (TON) or flavour (TFN). The assessment is made as a triangle or paired test, with unforced choice (the basic variant of the standard) or forced choice (Annex B), at 23 °C.

The short method answers whether the sample has an odour or flavour, or compares it with a specified threshold number; the full method determines the threshold number of the sample. The simplified qualitative method (Annex C) is used to detect abnormal odour or flavour and may be carried out by one assessor.

Applications

• Water intended for human consumption — odour and flavour "acceptable to consumers and no abnormal change" (Journal of Laws 2026, item 748)
• Migration waters from tests of materials and products in contact with drinking water
• Raw water and water from the distribution network — method chosen according to the type of water and national regulations
• Rapid detection of abnormal odour or flavour — simplified qualitative method (Annex C)

Key parameters

Standard

Standard number

PN-EN 1622:2006

Title (PL)

Jakość wody — Oznaczanie liczby progowej zapachu (TON) i liczby progowej smaku (TFN)

Title (EN)

Water quality — Determination of the threshold odour number (TON) and threshold flavour number (TFN)

Step-by-step procedure

1. Assessing the safety of the sample

   If harmful micro-organisms or toxic substances are suspected, the sample is not tested without further precautions; the risk of pathogens is assessed with appropriate biological methods before the flavour assessment — this is not necessary for waters disinfected with chlorine, ozone or UV radiation (clause 5).

2. Sampling and storage

   Into clean, well-stoppered glass bottles, without headspace; during transport and storage keep cool and dark, in a refrigerator at (4 ± 2) °C, as briefly as possible and at most 72 h — the storage time is stated with the result (clause 8).

   🌡 Temperature: 4 ± 2 °C

3. Dechlorination of chlorinated samples

   Chlorinated samples are dechlorinated with sodium thiosulfate or ascorbic acid according to normative Annex A; the standard refers to ISO 7393-2 (determination of chlorine).

4. Temperature equalization

   Bring the sample, the dilutions and the reference water to 23 °C in a water bath or incubator at (23 ± 2) °C; assessment in a room at the same temperature (clause 6, 7.2).

   🌡 Temperature: 23 ± 2 °C

5. Choice of method

   Short method — when checking whether the sample has odour and flavour, or comparing them with a specified threshold number; full method — when TON or TFN is determined. Variant with unforced choice (at least 3 assessors) or forced choice (Annex B, 8 assessors); triangle or paired test (clauses 1, 3, 9).

6. Assessment by the panel

   The assessors compare the sample or its dilutions with the reference water; flavour is assessed without swallowing the samples (clauses 4–5). Dilutions are prepared with reference water according to Annex F, and the course of both methods is described in 10.3 of the standard.

7. Result and report

   TON or TFN = (A + B) / A for the dilution beyond which odour or flavour ceases to be perceptible (clause 3); the sample storage time is stated with the result (clause 8).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Assessors do not swallow any sample (clause 5)
• Samples suspected of containing harmful micro-organisms or toxic substances are not assessed without further precautions; the risk of pathogens is assessed with biological methods — except for water disinfected with chlorine, ozone or UV (clause 5)
• When toxicity is suspected, the risk to assessors is evaluated on the basis of previous toxicity tests on the same or similar samples (clause 5)
• The standard does not address all safety problems — practices are established by the user, and the assessment is performed by suitably trained staff

Frequently asked questions