One hit wonder
Hi Peter, a cycle helmet is designed to absorb one major impact and then be thrown away, this way they can be made light and with plenty of cooling air flow. But for surfing or white water you need a helmet that can take multiple impacts, hence there are different CE standards and also why ski helmets have even tougher requirements than water helmets. So imagine being beaten up against the rocks and your helmets falls apart.... not so pretty. A good helmet is simply good health insurance.
James