Tap water, crop irrigation and other human uses around the world are using groundwater at 3.5 times the sustainable rate. In some cases, water is being sucked from aquifers (underground water-bearing formations) faster than new water can filter in. In others, “fossil aquifers” – formations that no longer replenish – are being used up. Solutions being explored include improving the efficiency of water use by agriculture and encouraging conservation in homes and businesses.