Aquaplaning/Hydroplaning
1. Take your tire pressure in kg / sq cm
2. Divide this by the specific gravity of the contaminant
3. Take the square root of this value
4. Mulitply this by 34
5. The result is the speed of aquaplaning in kts.
Source: Airbus "Getting to Grips with Aircraft Performance" Section 5.5.2.4, Page 82.