DD1 (2yr 8 months) has twice gone through a phase of hating baths and showers. She seemed genuinely frightened so we gently encouraged it without forcing anything and if she wasnt in to it, we just sponged her down in the bathroom with a flannel. Both times she came back to it, the first time took about 3-4 weeks, the second time 2 weeks.
Its totally normal of course for them to have fears and worries, all part of them exploring and discovering the world around them. Try to offer and encourage where possible without pushing or forcing it on him. Of course if they arent urgent things (i.e. he will shower so bathing might not be vital right now), just letting him get back to it in his own time is a good approach. Encouraging similar behaviour but in different circumstances is also good - i.e. water play outside
And try not to stress, it wont last forever