Abstract: Determination of water tariff has a goal to service to the community for the better. Tariff adjustment should always be done by a professional management rates. Rates must be constantly adjusted to inflation. PT. Tirta Lyonnaise field as a joint venture between Suez environment France and PDAM Tirtanadi Medan established a tariff formula that monthly payment-fixed operating expenditures+finance and investment costs+volumetric fee. Corporate debt originally in Euro converted into dollars. Both sides companies namely PT, Tirta Lyonnaise Medan and PDAM Tirtanadi Medan, agreed to refund the foreign debt in the Euro with domestic debt in the form of dollars, given the company’s overall revenues in the form of dollars. So, the calculation becomes more precise. Upon conversion of this debt goes well then US Dollar exchange rate and inflation does not affect the general United States again, the components used are inflation component of Medan and energy costs, chemical costs and the cost of raw water according to the actual cost of PT. Tirta Lyonnaise field. Changes in tariff system has recently been agreed by both parties and research conducted to date does not occur or disputes barriers that interfere with cooperation.