The sand-and-gravel aquifer system in the UAE is a mix of sand and gravel that holds groundwater. The water depth varies across different areas, with the eastern mountains being the main source of water recharge. Heavy use of groundwater in certain areas has caused water levels to drop. The water quality differs in different parts of the aquifer, with high nitrate levels in some areas due to farming activities. The water composition also varies, with different types of salts present in different regions. Overall, the eastern part of the aquifer has fresh water, but the coastal areas have saltwater intrusion, making the water salty.