Most homes have a customer gate valve which is typically located just beyond the meter between the meter and the house. The valve can be inside the meter box, but is usually outside the box housed by a 4 inch PVC pipe with a small round lid. This is known as a valve box. If you cannot locate a gate valve or if it is inoperable, you will need to call 512-401-5550 to have a technician dispatched to your residence to disconnect service on the city side.
The City shut off (angle valve) is located inside the meter box immediately before the meter. This valve is for City use only. Tampering with the valve or meter is a violation of Ordinance Number 82-18, and can be subject to prosecution.
Your cutoff valve is located in the round structure, in proximity to your rectangle-shaped water meter box. It may be labeled, "Property Owners Cutoff". Here is an example: