The title isn't entirely accurate, what Trump would do is completely dodge the question asked by the moderators in order to respond to something Biden said. His water comment was responding to Biden.
I don't remember what he said about climate change, I don't think he outright denied it though.
He reacted the same way to the question about starving children in the U.S. He immediately pivoted to something Biden said, rambled for almost the entire answer period and then proclaimed that of course he was going to do something about the starving children. For the last 30 seconds. After he was stopped and asked the question again.