The effective dose annual limit in European Union member states for doses above natural background is 1 mSv. This includes ingestion, inhalation and external dose to a member of public. For doses received due to ingestion of drinking water, parametric value for annual indicative dose is 0.10 mSv. As the name indicates, parametric value is not a limit value: when the parametric value is exceeded, a risk estimation needs to be carried out. Assessment of health risks is done in various fields, however, it is unclear how to do this for drinking water in a situation where the parametric value for indicative dose is exceeded but the annual effective dose limit is not. Approach for risk assessment through cost-benefit analysis is proposed to find the upper limit for investment in a water treatment plant that is justified for lowering the indicative dose of drinking water to a level equal to the parametric value. When a water treatment process cannot be improved with financial resources equal to or below the upper limit of investment, the risk caused by radionuclide ingestion with drinking water can be considered low enough that it is acceptable for the society as a whole. Case study based on the situation in Estonia is brought as an example.