The rules are more applicable to the rating of the current carrying capacity of the pvc cables. The maximum current rating of a pvc cable is based on the copper conductor attaining a temperature of 70 degrees C. If your water pipe temperature is approaching 70 degrees then there's every likelihood that the cables will fail being in such close proximity. Ideally either the cables or pipes should be moved away from each others sphere of influence. If this cannot be done suggest you fit insulation over the pipework to minimise heat transference, DO NOT repeat DO NOT fit insulation over the cables as this will impair the cables ability to remain cool when carrying rated current.