Can we install a new electric water heater on 200 amp electircal service?

Depends on the calculated connected load.

Easy answer is yes, as most 200 amp services can handle a water heater, however, we have no idea if your service has the capacity.

Also, we have no idea what size water heater you have.

Your question is WAY too vague.

On top of what TK accurately stated, what if you mean a whole house instant hot unit. Then the answer is most likely no.