I have a 220v hot water tank. I want to wire it with 110v. Can I hook up just one of the elements or something like that?

First, you have a 240 volt hot water tank.

Second, 240 volt is more efficient than 120 volt, so why would you want to change that?

To answer your question, some hot water tanks will allow a 240v source or a 120v source.

What do the electrical specifications for your water heater call for?

A 240 volt water heater has elements rated 240 volts, usually two elements.

If you want to use 120 volts, you will need to change out both elements with new ones rated 120 volts.

If you connect 120 volts to a 240 volt heater, it will not heat up sufficiently, it may barely get warm.