Irosin being located at the foot of the Bulusan Volcano mountain ranges have an abundance of water coming from numerous springs at the mountain slopes moving downstream to the creeks and rivers that converges at the Cadac-an River. The waters are utilized for residential, commercial and agricultural purposes. The volume of water discharges from the different springs supplying potable water to the residents of each barangay differ due to the varying condition of the watershed, water source and the type of water system installed. The total discharge of documented springs both utilized and for future sources was estimated to be 227 liters per second in 2013.
The 2013 water facilities in Irosin are categorized into Level I, Level II and Level III water supply system. Of the total 11,023 households documented in 2013, there are 11.7% with Level I water supply system of which 190 households are using shallow wells, 476 using deep wells and 62 using developed spring. About 47.2% of households have Level II systems and 40.2% of households have piped-in water supply. Seventy two percent of urban households have Level III connection. In terms of access to toilets, 71.8% of households have sanitary toilets, 6.7% have unsanitary toilets while 21.5% have no toilets.