Integrated water flow model is a computer program used to simulate the flow of land surface, surface water and groundwater. It is a rewrite of IGSM software. Iwfm program and source code are provided free of charge. It uses finite element method to simulate groundwater flow. Surface water flow can be simulated by a simple one-dimensional flow network or by moving wave method. Allows users to run models for a specific period of time while editing input files. Iwfm simulates four land use categories: agriculture, urban, native vegetation and riparian vegetation. Land use area is divided into a time series with corresponding evapotranspiration rate and water management parameters. In the agricultural and urban land use categories, iwfm applies surface water and groundwater according to a specific ratio, and can selectively adjust surface water and groundwater to meet water demand.