The Han River is the largest source of fresh water in Korea. It splits Seoul in half and is lined all the way through the city with parks and restaurants. The River is “supposedly” clean enough to swim in, but if the Koreans won’t swim in it, the rest of us better avoid it as well. While the water is chemically treated before arriving at your home and is fine for bathing and teeth-brushing, it’s drinkability is questionable at best.
Bottled mineral water is the drinking water of choice in Korea and can be bought absolutely everywhere for dirt cheap. A two-liter bottle will cost you a mere 900 won (90￠) at a local supermarket and a twenty-liter jug delivered to your home generally runs about 5,000 won.