The researchers studied water in the Kalaoya basin in Sri Lanka to understand how groundwater gets recharged. They looked at the isotopes in the water to figure out where it comes from. They found that the water in the upper part of the basin comes directly from rain in the higher areas. In the middle part, shallow groundwater and surface water contribute more to the groundwater. In the lower part, surface water plays a bigger role in recharging the groundwater. The researchers also found that the water from the Mahaweli diversion schemes is different from the water in the Kalaoya basin. Monitoring the isotopes in water over time can help us understand how groundwater gets recharged in the Kalaoya basin.