This article describes how to prevent water interference on PCAP Touchscreens

At times we receive inquiries from customers who are using their PCAP touchscreens in an environment where water droplets can make contact with the touchscreen. This sometimes causes the touch to stop working or working erratically. Is there anything that can be done about this?

Although PCAP is more water resistant than IntelliTouch (SAW), it is still vulnerable to water droplets - same as your smartphone, when it gets wet it does not work correctly until you wipe it off. This is because water conducts electricity the same as your skin does. PCAP stands for Projective Capacitive. 

Capacitive means: exhibiting or relying on electrical capacitance: touchscreens or smartphones with capacitive technology, react to electrical impulses generated by your finger, a conductive stylus, or other object that conducts electricity. 

Therefore whenever water or water droplets come in contact with the screen it emits a small amount of electricty which may cause the touch sensor to become erratic until it is dried off.

If you are using a touchscreen in an environment that may present a water issue you may want to consider using Elo's AccuTouch (resistive) technology which is not vulnerable to water droplets.

See how AccuTouch works.