According to examples of the disclosure there is provided a heat-driven pumping system and a method of pumping. The heat-driven pumping system comprises a closed circuit for a first liquid. The closed circuit comprises a vaporization portion. The vaporization portion is configured to receive heat from an external source. The vaporization portion is configured to cause vaporization of first liquid within the vaporization portion. Vaporization of first liquid within the vaporization portion thereby increases an amount of gas in the closed circuit. The closed circuit is sealed such that the increase in the amount of gas increases a pressure exerted on the first liquid. The heat-driven pumping system comprises a transfer means. The transfer means is configured to convert the pressure exerted on the first liquid into a pumping force. The pumping force is transferred to a pumping vessel for pumping a second liquid.