Wiring to Water Heater not getting 240v
With only 5v on the bottom breaker I would turn them off and then pull the breaker and look at the buss terminals. Are they bright and shiny, or possibly melted away?

Inspect the breakers also; if no damage is found with the breaker out of the panel, close it and measure the resistance from where the wires connect to the back of the breaker. This should be very low, close to zero. If the reading is high the breaker may be bad.

As a possible temporary quick fix, cycle the breaker 10+ times on/off. Many times this clears carbon arcing and reseats the hammers, check resistance, if it dropped the breaker will usually work for a while (until you get a replacement). 

If the breaker still shows a high or open resistance and no pitting or arcing on the buss bar, replace the breaker. 

Make sure to always open or turn off a breaker prior to removing or installing so there is less chance of an arc flash.