I think you can apply both in case of drinking water. From heavy metal pollution indices we can assume the chance of health risk (carcinogenic and non-carcinogenic effect) on human body.
You can use these heavy metal indices for determining the water quality in terms of health risk. However, you can also use some other analysis like CR, HQ for carcinogenic risk assessment.
You can follow these articles -
Book Non-carcinogenic and Carcinogenic Health Risk Assessment of Metals
Article Applied Heavy Metals Pollution Index (HPI) as a Water Pollut...