hope this schematic helps to get a better understanding of the final circuit for my project "DIY Water Touchpad"

Did you add any salt to the water to make it more conductive?

 

Did you add any salt to the water to make it more conductive?

Salt must NOT be added to the water in order to minimize electrolysis, since electrolysis will disturb the uniform composition of water, hence, the conductivity will not stay constant at all points inside the water

 

I can't tell from the drawings, but are you using DC between the electrodes?

 

I can't tell from the drawings, but are you using DC between the electrodes?

The polarity of voltage drop across the water is constantly swapped over by the Arduino Uno to minimise the electrolysis.