Septic / OSSF
Septic Systems in Unincorporated Areas Require a Permit
If your San Patricio County property is outside city limits and has no public sewer, you need a state permit for your septic system.
In Texas, any property without a public sewer must have an On-Site Sewage Facility, or OSSF. Most people just call it a septic system. State rules say you need a permit before you install, replace, or make big changes to one. In many counties, the county itself issues the permit under oversight from TCEQ — the Texas Commission on Environmental Quality.
Before buying rural land in San Patricio County, ask whether an existing permitted OSSF is already in place. Also check whether the soil and lot size can support one. Sandy or clay-heavy soils near the coast can make septic systems harder and more expensive to install.
Contact the San Patricio County environmental health office or TCEQ's OSSF program. They can tell you who issues permits in your area and what a site evaluation involves.
Source to confirm: TCEQ — On-Site Sewage Facilities for Homeowners