A continuous method for the separation of charged particles from a stream of water in a device comprising a first channel adapted to contain a gas separated by a first gas permeable wall from a second channel, the second channel comprising one inlet and at least two outlets, the second channel being separated by a second gas permeable wall from a third channel, the permeable walls (12, 14) permitting the transfer of a gas from the first channel through the first gas permeable wall to the second channel and through the second gas permeable wall to third channel; the method comprising: flowing the stream of water and charged particles through the second channel from inlet to outlets, supplying a pressurized gas comprising CO 2 to the first channel to pressurise the first channel, whereby CO 2 flowing into the first gas channel passes through the gas-permeable wall, operating the device with a pressure of the CO 2 in the third channel being lower than the pressure of the CO 2 in the first channel to establish a pressure gradient of the soluble gas within the water, thereby causing the formation of ionizable species within the water resulting in an ionic concentration gradient within the water causing the migration of the suspended charged particles transverse to flow direction due to diffusiophoresis to different regions within the flowing suspension, whereby the flow entering a first outlet (20b1) of the second channel receives a lower relative concentration of the charged particles than originally present at the inlet, and the flow entering a second outlet (20b2) of the second channel receives a higher relative concentration of the charged particles than originally present at the inlet, the charged particles having a net positive or negative charge when present within the liquid when within the device. a first channel adapted to contain a gas separated by a first gas permeable wall from a second channel, the second channel comprising one inlet and at least two outlets, the second channel being separated by a second gas permeable wall from a third channel, flowing the stream of water and charged particles through the second channel from inlet to outlets, supplying a pressurized gas comprising CO 2 to the first channel to pressurise the first channel, whereby CO 2 flowing into the first gas channel passes through the gas-permeable wall, operating the device with a pressure of the CO 2 in the third channel being lower than the pressure of the CO 2 in the first channel to establish a pressure gradient of the soluble gas within the water, thereby causing the formation of ionizable species within the water resulting in an ionic concentration gradient within the water causing the migration of the suspended charged particles transverse to flow direction due to diffusiophoresis to different regions within the flowing suspension, whereby the flow entering a first outlet (20b1) of the second channel receives a lower relative concentration of the charged particles than originally present at the inlet, and the flow entering a second outlet (20b2) of the second channel receives a higher relative concentration of the charged particles than originally present at the inlet, the charged particles having a net positive or negative charge when present within the liquid when within the device.