As I knew, the delta-rawcount caused by water flow is similar to finger touch. Hence it's difficult to identify water flow and finger touch.
In TrueTouch product, we use the combination of Mutual and Self CapSense methods to detect if it is water or finger, as touch will lead to rawcount increasing for both Mutual and Self. But water flow will lead to rawcount decreasing of Mutual and increasing of Self.
However, I didn't do such an experiment on PSoC4/MBR CapSense...not sure if it can work.
Another thing is Shield sensor, shield sensor is able to separate finger touch with liquid mist, but may not work on identifying liquid flow...
Further more, if there are more than 3 buttons in your application, you can make a 'multi' touch filter, if more than 3 buttons or more become 'ON', mark it as "water flow" touch, ignore the touch report until 'water flow' removed.