A system for dissolving a first gas in DI-water, the system comprising: a deionized water source; a gas mixing device comprising: a first inlet suitable for being in fluid communication with a first gas source for supplying the first gas; a second inlet suitable for being in fluid communication with a second gas source via a valve for supplying a transfer gas; and a mixed gas outlet for outputting a gas mixture comprising the first gas and the transfer gas; a contactor comprising at least one inlet and at least one outlet, the contactor in fluid communication with the deionized water source and the mixed gas outlet via the at least one inlet of the contactor, the contactor generating deionized water having the first gas dissolved therein; a sensor in fluid communication with the at least one inlet of the contactor for measuring a flow rate of the deionized water; and a controller in communication with the sensor, the controller configured to set a flow rate of the first gas supplied from the first gas source based on: i) the flow rate of the deionized water measured by the sensor, and ii) a predetermined conductivity set point; characterized in that the first gas is ammonia gas, and the controller is further configured to adjust a pressure of the transfer gas output from the second gas source via the valve based on the flow rate of the deionized water measured by the sensor, and the system further comprises a pump in fluid communication with the at least one liquid outlet of the contactor for pumping the deionized water having ammonia gas dissolved therein from the contactor. a deionized water source; a gas mixing device comprising: a first inlet suitable for being in fluid communication with a first gas source for supplying the first gas; a second inlet suitable for being in fluid communication with a second gas source via a valve for supplying a transfer gas; and a mixed gas outlet for outputting a gas mixture comprising the first gas and the transfer gas; a first inlet suitable for being in fluid communication with a first gas source for supplying the first gas; a second inlet suitable for being in fluid communication with a second gas source via a valve for supplying a transfer gas; and a mixed gas outlet for outputting a gas mixture comprising the first gas and the transfer gas; a contactor comprising at least one inlet and at least one outlet, the contactor in fluid communication with the deionized water source and the mixed gas outlet via the at least one inlet of the contactor, the contactor generating deionized water having the first gas dissolved therein; a sensor in fluid communication with the at least one inlet of the contactor for measuring a flow rate of the deionized water; and a controller in communication with the sensor, the controller configured to set a flow rate of the first gas supplied from the first gas source based on: i) the flow rate of the deionized water measured by the sensor, and ii) a predetermined conductivity set point; characterized in that the first gas is ammonia gas, and the controller is further configured to adjust a pressure of the transfer gas output from the second gas source via the valve based on the flow rate of the deionized water measured by the sensor, and the system further comprises a pump in fluid communication with the at least one liquid outlet of the contactor for pumping the deionized water having ammonia gas dissolved therein from the contactor. i) the flow rate of the deionized water measured by the sensor, and ii) a predetermined conductivity set point; characterized in that the first gas is ammonia gas, and the controller is further configured to adjust a pressure of the transfer gas output from the second gas source via the valve based on the flow rate of the deionized water measured by the sensor, and the system further comprises a pump in fluid communication with the at least one liquid outlet of the contactor for pumping the deionized water having ammonia gas dissolved therein from the contactor.