NEW DELHI: Almost 22 per cent of the groundwater in the country has either dried up or is in the critical category, Jal Shakti Minister Gajendra Singh Shekhawat said on Friday underscoring the need to use the resource judiciously. The government has also started the work of mapping aquifers and by next March, it will cover mapping of all the critical districts in the country, he said.An aquifer is an underground water resource that helps store and release water."Our dependence on groundwater is 65 per cent. It is not infinite. It is invisible, so we don't know how much water is being used."Almost 22 per cent of ground water has either dried up or is in the critical category. The government is mapping aquifers," Shekhawat said at an event here.Central Ground Water Board Chairman K C Naik said of the 25 lakh square kilometres area where groundwater level can be mapped, 10.8 lakh sq km has been covered."We are committed to complete it in critical districts by March," Shekhawat added.A Memorandum of Understanding was signed between Central Groundwater Board and the MARVI system (Managing Aquifer Recharge and Sustaining Groundwater Use through Village-level Intervention) that comprises NGOs working in the area of water conservation.