For fast, simple detection of water on surfaces or in non-polar solvents - turns from white to pink when water is present.
Ideal to check for water contamination in gasoline or petrol.
On contact with water the paper changes from white to pink. The reaction is not reversible, even after drying the colour change and contact with water can be proved.
The paper can be used to test the leak tightness of tubing or to detect condensed water. It can also be used to check if sensitive products like electronic components have come into contact with water.
In chemical laboratories the paper can be used to check that solvents are truly anhydrous - dip a piece of the paper into the solvent. If it remains white after the solvent has evaporated, then it is anhydrous.
To detect water vapour in gases, moisten the paper with isopropanol and then direct the gas stream onto the paper and observe for any colour change.