I have recently switched to cold water for most of my laundry. However, I’ve found that the clothes smell musty if I don’t get them out of the washing machine as soon as they are done. A solution that I’ve found is to put a capful of ammonia in the wash water. It seems to kill whatever bacteria are causing the odor, and my clothes are a lot fresher. You might give it a try if you are cutting back on your hot water usage.