Question on domain name impact on email address

All,

I am setting up a new Exchange 2013 server to replace an old GroupWise server. Forgive my ignorance but I am new to Exchange.

My AD root domain is like this "LHISD.WATER.TX.NET". The Edir is set as "WATER.TX.NET"

So with our GroupWise Server a users email is like JoeP@WATER.TX.NET. Can I use the same format even though the Exchange server is in a root domain called "LHISD.WATER.TX.NET", or am I stuck withJoeP@LHISD.WATER.TX.NET ?