Is your Austin utility bill’s drainage line higher than you expected, or did it jump after you poured a new patio or widened the driveway? You are not alone. In 78745, your monthly drainage charge is tied to how much hard surface your lot has because those surfaces shed stormwater into the public system. In this guide, you will learn how impervious cover drives the charge, how common projects in South Austin affect your bill, how to estimate changes before you build, and what steps can help reduce costs over time. Let’s dive in.

How the drainage charge works

Austin funds stormwater management and flood mitigation through a drainage utility charge. For single‑family homes, the City estimates the impervious area on each parcel using GIS mapping and aerial imagery. The more impervious cover you have, the more runoff your property generates and the higher your drainage charge.

The charge updates periodically. It can change after permitted projects that add roofs or paving, during citywide mapping refreshes, or when you request a review of your parcel data. The City publishes the current rate schedule, so you should confirm the latest rate before running numbers. You can review the program overview on the City’s page that explains the drainage charge and how it is calculated.

What counts as impervious cover

Most hard surfaces that do not absorb rain are counted. Common examples include:

• Roofs and roof overhangs from additions
• Concrete or asphalt driveways and aprons
• Solid patios, pool decks, sheds, garages, and sidewalks

Some materials can be considered pervious or partially pervious if they are designed and installed to City standards and properly documented. These may include permeable pavers, gravel with an open base, vegetated swales, and mulch areas. Simply installing “permeable” pavers is not enough. The City may require engineering documentation and inspection before treating those areas as pervious for billing.

Check your current mapping and bill

Before you plan a project or appeal, confirm what the City currently shows for your property:

• Review your Austin utility bill for the drainage charge details. The City’s Utility Billing page explains billing basics and how to contact customer service.
• Use the Austin Property Profile GIS viewer to view parcel data and aerial imagery for a quick sense of your impervious area.
• If the mapping looks off, you can request a review. Be prepared to provide photos, site plans, or a survey, and expect the City to verify conditions.

Estimate your bill change before you build

You can ballpark the impact of a new patio, driveway, or addition with a simple process:

1. Measure the project area. For a patio, measure length times width to get square feet. For an addition, use the roof footprint.

2. Find the current City drainage rate for single‑family parcels. Check the City’s drainage charge explanation or contact Austin Water for the latest rate.

3. Multiply added square feet by the rate. That gives you the annual increase. Divide by 12 to estimate the monthly impact.

Example method: If you plan a 300 square foot concrete patio, you would multiply 300 by the current City rate to estimate the annual change, then divide by 12 for a monthly estimate. If you substitute a qualifying permeable system and document it to the City’s standards, you may reduce or offset that increase.

Credits and ways to reduce the charge

Austin provides ways to reduce drainage charges when you manage runoff on site with approved stormwater control measures. These reductions are not automatic. You must apply, document the design, and maintain the system to keep the credit.

Measures that may qualify

• Rainwater harvesting or cisterns sized to capture roof runoff
• Properly engineered permeable pavements or paver systems
• Vegetated swales, rain gardens, or infiltration trenches that receive runoff
• Disconnecting roof downspouts to pervious areas for infiltration
• Green roofs or intensive vegetated roof systems
• Conserving open space and planting trees that increase infiltration

For eligibility, design requirements, and applications, refer to the City’s Watershed Protection Department. For general background on how green infrastructure reduces runoff, you can also review the EPA’s overview of green infrastructure. Local rules govern whether a measure earns a credit, so always confirm City criteria before you build.

How the credit process works

• Application. Submit the City’s required forms with design plans, calculations, and manufacturer documentation.
• Documentation. Keep construction records and as‑built drawings. These help the City confirm performance and determine your credit.
• Inspection and maintenance. Expect initial verification and ongoing maintenance to keep the credit. Some programs require periodic recertification.

Credits can offset part of the drainage charge. The cost benefit varies. For smaller projects, the application effort and maintenance can outweigh savings. For larger additions or extensive driveways, the savings can be more meaningful over time.

Fix mapping errors or appeal

If you believe the City’s mapping overstates your impervious cover, you can request a review through Austin Water or Watershed Protection. Provide evidence such as photos, surveys, or as‑built plans. The City may verify in the field or update imagery and GIS data. You can start with Utility Billing for account support and be directed to the right department for a formal review.

Permits and timing in 78745

Most additions, driveways, and major grading in 78745 require a permit. Permits create a record that alerts the City to update your parcel’s impervious area after final inspection or during the next mapping cycle. Ask your contractor or the City’s Development Services team how your project’s impervious area will be documented, and what erosion and temporary stormwater measures are required during construction.

Timing varies. Some updates post soon after permit closeout. Others appear during the next citywide aerial update. If you need clarity, contact Austin Water for account‑specific timing.

Design tips to manage costs

You can often meet your design goals and manage your drainage charge at the same time:

• Prioritize infiltration and retention. Use rain gardens, infiltration trenches, or cisterns to capture runoff from new hardscape.
• Favor pervious materials when feasible. Choose engineered permeable pavers or open‑graded gravel with a designed base, and document them so the City recognizes the benefit.
• Limit new roof footprint when possible. Consider smaller additions or alternatives like trellises instead of enclosed square footage if managing impervious cover is a priority.
• Combine functions. Route downspouts to planted areas or cisterns rather than directly to driveways or storm lines.
• Get documentation right. Accurate permits and as‑built records speed mapping updates and credit eligibility.
• Run a simple payback. Compare upfront cost of stormwater measures to the expected annual drainage charge reduction using the City rate.

Buyer and seller tips for 78745

If you are buying in 78745:

• Review the seller’s recent utility bills to understand the current drainage charge.
• Walk the site and compare it to the City’s GIS imagery. Look for new patios, driveway expansions, or additions that may not be reflected yet.
• If you plan improvements, estimate impervious area changes and factor them into your operating budget.

If you are selling in 78745:

• Gather plans and permits for any additions or hardscapes. Buyers appreciate clarity on what the City is likely to show for impervious cover.
• If you installed permeable systems or rainwater harvesting, organize documentation and maintenance records. These can support buyer confidence and potential credits.
• Correct mapping errors before listing if possible. Accurate records reduce surprises during escrow.

By approaching impervious cover like any other property utility factor, you protect your budget and reduce risk during a project or a transaction.

Ready to plan a project or evaluate a property with drainage charges in mind? Reach out for research‑backed guidance, local context, and a practical action plan tailored to your goals. Unknown Company is here to help.

FAQs

Do small patios in 78745 raise my drainage bill?

• Yes. If a patio increases your measured impervious area, your drainage charge increases. Estimate the impact by multiplying added square feet by the City’s drainage rate.

Do permeable pavers avoid the drainage charge in Austin?

• Not automatically. The City requires specific design, documentation, and sometimes inspection before treating a surface as pervious for billing.

When will my charge update after a permitted project?

• Often after permit final and the City’s mapping update. Timing varies by project and mapping cycle. Contact Austin Water for account‑specific timing.

Can I appeal the impervious area Austin shows for my lot?

• Yes. You can request an impervious cover review and provide evidence such as photos, surveys, or as‑builts. The City may adjust your parcel data after verification.

Are drainage charge credits worth it for a typical 78745 home?

• It depends. Larger roof additions or driveway projects may see meaningful savings from approved stormwater controls. For small projects, costs and maintenance may outweigh the benefit.