Art,

While I don't know how much you pay per kw hr. more than $100 increase
suggests a huge amount of electricity. Go to your electric meter, look at
the spinning disc, now pull the breaker for the water heater, go back and
look at the spinning disc, repeat this for all of the breakers in your box,
and keep notes. Repeat this in about an hour. Now see which circuits caused
the most "spinning". This should focus you on possible sources of the
problem.
Another possibility is an error in meter reading sometime in the last few
months.

Good luck,
Dave M.