Cumulative health risk estimation for exposure to mixtures is a current issue, which would present a useful tool for environmental and public health management. Cumulative risks were estimated with response and dose addition methods for individual multi-route -multi-pathway exposure to trihalomethanes and associated carcinogenic toxic risks in Izmir, Turkey. Exposure levels were estimated for ingestion, dermal, and inhalation routes using measured tap water and bottled water THM concentrations. Drinking, showering, hand and dish washing were the considered pathways. THM concentrations in air during the showering were modeled with two-resistance theory using tap water concentration data. The estimated carcinogenic risk levels for ingestion route were in the range of safe (< 10 −6 ) to low priority (< 10 −4 ), for dermal route all were in the safe zone (< 10 −6 ), and for inhalation route were in the range of safe to high priority (> 10 −4 ) zones, indicating ingestion and inhalation routes were of similar significance ahead of dermal exposure. Cumulative carcinogenic risks of THM compounds were estimated using simple (response) addition and dose addition using cumulative relative potency factor (CRPF) methods. CRPF method estimated the risks at lower levels compared to the simple addition, which originated from the use two different risk factor values for the index chemical in the method. Cumulative chronic-toxic risks were also assessed, rendering below the threshold risk levels for all routes. This study showed that multi-route -multi-pathway exposure assessment and cumulative risk assessment should together be considered for better environmental and public health management.