The Hydrogeological Model of Latvia (LAMO4) was developed by the Environmental Modeling Centre (EMC) of Riga Technical University (RTU). The model provides an electronic data set on the geological structure, on groundwater heads and flows, interaction with the hydrographic network (rivers, lakes) and atmospheric precipitation. LAMO4 can be used to identify groundwater resources and assess their protection against pollution. It is possible to calculate the amount and movement of pollution and to model remediation measures for contaminated sites. LAMO4 is a regional data source for detailed local hydrogeological models. The identification of groundwater resources requires a balance of groundwater flows. The balance obtained by LAMO4 shows how the groundwater resources are replenished by atmospheric precipitation and how much of the replenishment enters rivers, lakes, operational wells and crosses the borders of Latvia or local water bodies.