Did i imagine or is it true that you are breaking the law splashing a pedestrian when you drive past in floods

It may be fun, but it also can be driving without due care and attention for the safety of other road users. Yes pedestrians do count! Fine and 3 points unless you can show you couldn't reasonably avoid it. The damp pedestrian could also sue you for damage to clothing and possessions. If blocked drainage was involved then the local road authority could be dragged in as well