Water losses in a designed irrigation area for paddy fields is necessary to be examined. Water losses in conveyance canal consists of evaporation and infiltration. The infiltrating water becomes groundwater storage and is distributed along the canal.

Semi-empiric equation of infiltration on canal was developed by Moritz (1913) and the semi-graphic equation was developed by Bouwer (1965). Forchheimer (1930) has developed a formula based on dynamic balance of water flow to calculate the permeability coefficient value of soils and was continued by Dachler (1936) and Sunjoto
(2002) that computed the shape factor of a well based on those formulas. Further, it can be developed a formula of water losses in the conveyance canals to complete the two existing formulas of Moritz and Bouwer.

This research aimed to get a field data and had measured water losses directly in the canal of Sukawati Irrigation Region in Comal, Central Java, Indonesia. The results of the measurement are compared to the calculating results derived from the three formulas of Moritz, Bouwer and the proposed formula, based on the field data and for soil coefficient of permeability is 8.333 × 10–6 m/s. An analysis of the result is conducted using a least square and linear regression method. The result of the comparison are as follows: the proposed formula has the smallest deviation, followed by the Bouwer formula in the middle, and finally the Moritz formula has the biggest deviation.