It seems that the ICAO 'Water patches' is equivalent to 'contaminated' in Jar-ops and presumably under EU -Ops also, which is >3mm water over 25% of RW (or by slush or looses snow equivalent to >3mm, or compacted snow or wet ice) (Paraphrased)
Ahh, beware Dumbledor, I quoted what the UK books say. ICAO is not nearly as specific - Annex 14 simply says:
2.9.4 Recommendation.— Whenever water is present on a runway, a description of the runway surface conditions on the centre half of the width of the runway, including the possible assessment of water depth, where applicable, should be made available using the following terms:
DAMP — the surface shows a change of colour due to moisture.
WET — the surface is soaked but there is no standing water.
WATER PATCHES — significant patches of standing water are visible.
FLOODED — extensive standing water is visible.
And note that this is only a recommended practice. Maybe there is more written in other docs but I'm not aware of it.
BTW, I found the UK AIP entry that I was looking for - its para 15 in
AIP link. It's more specific about the implications for performance calculations and accords with your comments on EU-Ops.