Water provider?

I'm trying to sign up for trash/water for a new house that I'm closing and moving into later this week. The information provided by seller is that trash and water is serviced by city of Houston, which is what I expected. I tried to sign up on Houston Public Works (https://www.houstonwaterbills.houstontx.gov/ProdDP/Default/Default) and it told me that my address is not in the system. I then called the customer service number, the agent told me that they do not service my address and that I can try calling 311 to find out the subdivision's water info. I called 311 and the agent was going to transfer me to the water department but after waiting for 10 mins it just disconnected.

I will try calling again, but I'm really confused. I thought water is serviced by city of Houston? Why are they telling me that they don't service this address? The house is three years ago so it's not because the address is new. Could someone educate me on this please? I will call 311 again and if that doesn't work I will contact the seller to get more info, but just really confused.