squeeze your butt for a few seconds then release and repeat. you can do it anywhere, in the office, in the car, on the crapper..and for abs you can tighten your abs then release and repeat..those exercise do not compensate in any way for a gym workout but they certainly are a way to keep circulation and keep your muscles going when you are stationary
the thing about the water temperature is a myth, doing that will only burn a couple calories. you can do squats and stationary lunges while in the shower, you can also do those things while brushing your teeth and washing you hands, it adds up!
To tell you the truth you can t do that in the shower. I recommend a gym
