During the Chilean summer of 2008, a study was carry out to evaluate potential infiltration losses of the Laja-Diguillin irrigation-canal in four sections of rivers that are use for irrigation water conduction. The four rivers are Polcura, the upper part of the Laja, the Huepil (Itata) and a small section of the Diguillin. To evaluate infiltration losses, a three-month field campaign was done to study the rivers, measure flow rates, infiltration rates, implement observation wells and water sampling for chemical analysis. A conceptual hydrogeological model was establish and was used to validate the conclusions obtained from a monthly water balance model. Irrigation water conduction losses at the Polcura and the Upper Laja rivers are approximately 1.4 m(3)/s. That water feeds the aquifer located at the middle section of the Laja River. Infiltrations at the Huepil River are compensated by exfiltration from the aquifer. Losses at the short section of the Diguillin River are negligible.