Threshold Odor Number Calculator

TON equals sample volume plus odor-free volume over sample volume

Solution

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How It Works

The Threshold Odor Number measures how much odor-free water you need to add to a sample before the smell becomes barely detectable. A higher TON means a stronger odor. The test progressively dilutes the sample until a trained panel can just notice the smell, then calculates TON = (A + B) / A, where A is the sample volume and B is the odor-free dilution volume.

Drinking water standards typically require a TON of 3 or less. Industrial source waters can have TONs exceeding 200 before treatment.

Example Problem

A panel detects odor at the threshold when 50 mL of sample is diluted with 150 mL of odor-free water. What is the TON?

  1. TON = (50 + 150) / 50 = 200 / 50
  2. TON = 4

A TON of 4 exceeds the typical drinking water limit of 3 and would require activated carbon treatment or other odor control.

Frequently Asked Questions

What is an acceptable threshold odor number for drinking water?

Most drinking water standards set a maximum TON of 3. This means the sample can be diluted three-fold before the odor becomes undetectable. Water with TON above 3 typically triggers consumer complaints.

What causes odor in drinking water?

Common causes include algal blooms (earthy/musty smell), hydrogen sulfide from anaerobic conditions (rotten egg), chlorine or chloramine disinfection byproducts, and industrial contamination. Activated carbon and ozone are effective treatment options.

How is the TON test performed?

A trained sensory panel sniffs a series of dilutions at 60°C. Each dilution is compared to an odor-free blank. The threshold is the lowest dilution at which the panel consistently detects the odor, and the TON is calculated from that dilution ratio.

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