To ensure low leakage current and low dielectric absorption, the feed back capacitor should be made of a suitable dielectric material such as poly styrene, polypropylene, or Teflon.

Applications for Measuring Voltage from High Resistance Sources: Capacitor dielectric absorption and electrochemical measurements.

As noted initially, the capacitance depends on the dielectric properties of the water and the size and separation of the conductive elements forming the water capacitor.