Water is undoubtedly one of the most important resources for life on the Earth and groundwater is the primary source of drinking water in most developed countries. The advantage of using underground water for water supply is that it is naturally of better quality and it is better protected from direct pollution than surface water, which is why its treatment costs are lower. However, the biggest disadvantage is the cost of exploitation due to the fact that boreholes and wells have to be drilled to allow access to it (in some cases at great depths). Specific research is also needed in order to observe the trend of groundwater movement and to plan its protection. Therefore, groundwater monitoring is becoming an increasingly important activity in order to timely detect changes in groundwater levels and potential pollution. Monitoring is often expensive, therefore there are legal regulations and guides that define where, how and when groundwater should be monitored and which also determine limit values forpollutants.. This paper provides an overview of the legal regulations that prescribe the methods of groundwater monitoring in the Republic of Croatia, and it also presents practical examples which show the situation with groundwater in other countries and how they implement the process of monitoring.