Houston was built on mud. Some areas are in the 100 year flood areas and therefore a lender may require that you have flood insurance. 

Click here to see flood maps used by your insurance agent.

 The darker shaded areas are more prone to flooding.

If flood insurance is not required and not in a flood area, then flood insurance is much less expensive and you might consider buying it to be prudent and safe. Sometimes it floods in areas which are not designated as being in the 100 year flood plain.