Page 7: Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Formaldehyde
Rationale
A guideline value for formaldehyde in drinking water, based solely on health considerations, can be derived from the TDI as follows:
Figure 2. Tolerable daily intake (TDI) equation
where:
- 0.15 mg/kg bw per day is the TDI, as derived above
- 70 kg is the average body weight of an adult
- 0.05 is the proportion of total daily intake allocated to drinking water (as most of the exposure to formaldehyde is from food [89%, as calculated from data in the "Exposure" section] and less than 2% is from water, an allocation of 5% of the TDI to drinking water is considered appropriate)
- 1.5 L/d is the average daily consumption of drinking water for an adult.
A health-based guideline value of 0.35 mg/L (350 µg/L) for formaldehyde in drinking water can thus be derived. However, because this concentration is more than 25-fold higher than concentrations normally found in water supplies (1.2-13 µg/L), it is not considered necessary to establish a maximum acceptable concentration (MAC) for formaldehyde in drinking water.