If, when you stamp your foot on the ground the water splashes up, consider the surface contaminated – depending on the area covered.
Pre departure, get the first officer to do the test.
Before landing use ATC, line maintenance, etc, etc; OK we should use the official reports but every bit of info helps.
A further problem with the condition of the runway is how to correlate the range of wet surfaces with the landing performance. The baseline friction value might only apply to a thin film of water – depending on surface texture, but what is the loss of performance between that and 3mm (contaminated)?
On a ‘WET’ runway it’s useful to check the landing distance required for both wet and contaminated conditions, the latter particularly important for non-grooved and rubber contaminated surfaces. You can then choose one or the other or a safety buffering middle value.