There is a Stormwater Management Discount for both residential and commercial properties. The discount is for stormwater controls, such as rain gardens, rainwater harvesting or ponds, that exceed the legal requirements for development. Find out more about the discount program.

In addition, if you have an uncovered wooden deck and an unpaved portion of your driveways, we may be able to lower your impervious cover, which will in turn lower your bill. If you have these features, please call 512-494-9400 and ask about an administrative review of your drainage charge.

The following groups are exempt from the drainage charge:

  • The state
  • Counties
  • Independent school districts
  • Universities
  • Religious organizations that participates in a specific program to provide housing for the homeless.

Additionally, properties without any impervious cover will not be billed a drainage charge, and the charge does not apply to properties outside the city limits.

Residential customers may request a reduced drainage charge based on financial need through the Customer Assistance Program. This discount on the drainage charge is only available to those being billed directly by the City for drainage. It is not available to residents of multifamily dwellings for which the property owner or owner’s agent pays the drainage charge.

If you rent a single-family home, duplex, triplex, fourplex or garage apartment, you will be charged for drainage on your electric bill. When there are multiple units, such as a duplex, we divide the charge evenly among the units.

If you rent an apartment in a complex with more than four units, we will charge the property owner or manager for the whole property. They may choose to allocate the charge to their tenants keeping in mind any applicable provisions in the lease agreement as well as the requirements in City Code Chapter 15-9 (Utility Service Regulations).

In general, the answer is yes. Stormwater runoff generated by impervious cover continues to occur whether or not the property is vacant. In addition, the City is striving to keep uncollected charges from vacant properties to a minimum to keep the rates as low as possible for everyone.

The process is different depending on whether the owner or the tenant(s) are paying for utility services. Tenants may be paying for utilities in single-family residences, duplexes, triplexes, fourplexes and some commercial properties.

If the owner of the property is paying for utilities, and shuts utilities off for vacancy reasons, the drainage charge will remain as a charge to that owner.

If tenants on a property are paying the drainage charge and call to shut down their utility account, then the charge will be transferred to the owner of the property, whenever possible. There may be situations where the property is vacant for only a short period of time and we are not able to bill the owner in the limited time.

City Code section 15-2-12 and City Code Chapter 15-9 Article 12 provide a process for requesting a review of your drainage charge and for adjusting your drainage charge, if warranted. The process includes an administrative review by the Director of the Watershed Protection Department and an administrative hearing by a hearings officer. There is more information about this process on the Drainage Charge Administrative Review web page.

Please call 512-494-9400 to initiate your request for administrative review.

The adjustment factor is based on the percent of impervious cover on an individual property. It adjusts the drainage charge upwards for properties with more than 52.3% impervious cover and downwards for those with less than 52.3% impervious cover.

It is calculated for each property using this formula:

Adjustment Factor = (1.5425 x percent impervious cover) + 0.1933

The formula for the adjustment factor is based on the “weighted” average percent of impervious cover for the entire city, currently estimated at 52.3%. A weighted average is a more accurate way to calculate an average when the items being averaged are of relative importance to each other.

The City of Austin will calculate your drainage based on the following formula:

Monthly Drainage Charge = Monthly Base Rate x Impervious Cover x Adjustment Factor

Monthly Base Rate

The monthly base rate is $0.00514 per square foot of impervious cover. 

Impervious Cover

The impervious cover for each property includes surfaces like rooftops, driveways, parking lots, walkways, patios, unpaved driveways and unpaved parking. The City has measured the impervious cover for each property through its aerial data and mapping software, supplemented with zoning and development records.

Adjustment Factor

The adjustment factor is unique to each property and is based on the percent of impervious cover. It is calculated with the following formula:

Adjustment Factor = (1.5425 x Percent of Impervious Cover) + 0.1933


Drainage is “stormwater” that does not soak into the ground. It refers to water that falls as rain and runs off the land, and especially off of pavement or structures placed on the land. The City’s drainage system handles this water, and it consists of pipes, inlets, culverts, street gutters, ditches, channels, creeks, lakes, ponds, dams, tunnels and floodwalls.

Drainage can be a problem because of flooding, erosion and impacts on water quality. The drainage charge pays for programs that prevent, mitigate and/or correct these problems.

The drainage system should not be confused with the sanitary sewage system, which takes away water used in homes, businesses and industries for toilets, sinks, showers, washing machines and various types of business processes. The sanitary sewer system is a different system of pipes and infrastructure that lead to a wastewater treatment plant.

The stormwater drainage charge is shown on your monthly utility bill in the Drainage Service section. It funds the City of Austin's drainage utility mission and is authorized by the Texas Local Government Code.

The drainage charge was first adopted in 1982, the year after the 1981 Memorial Day Flood, which killed 13 people and caused $35.5 million in damage.

The drainage charge pays for a wide variety of programs to help with flooding, erosion and water pollution across Austin. Many projects and programs are working quietly behind the scenes to protect lives, property and the environment. Crews clean trash and debris from Lady Bird Lake, maintain our drainage infrastructure, and respond to more than 3,000 service requests annually. Staff respond to the pollution hotline about environmental spills and emergencies 24-hours a day. They coordinate numerous projects to help reduce the risk of flooding and erosion. Many of the programs, services and projects listed on the Watershed Protection Department web site are funded in whole or in part by the drainage charge and would not be possible without the charge.

Some projects that are funded entirely or in part by the drainage charge include:

  • ATXfloods and closing of flooded low water crossings
  • Restoration of the Shoal Creek Peninsula along Lady Bird Lake
  • Boggy Creek Greenbelt Streambank Restoration
  • Combating hydrilla on Lake Austin
  • Buyouts of flood-prone properties

The rate structure for the drainage charge is based on the impact that buildings and other improvements on a property have on Austin’s drainage system. It is important to note that the charge is based on the impact to drainage by manmade structures, not naturally-occurring drainage. State Code only allows municipalities to charge properties that have a structure or other improvement on it. Undeveloped properties are exempt from a charge.

The City is using both the amount and the percent of impervious cover on each property to calculate the charge because using both these parameters provide a very accurate basis for determining the proportional impact of each property to the drainage system.

The City completed a Stormwater Runoff Study in 2008. During the more than two decades of this study, staff collected measurements for 36 monitoring stations citywide. The study indicated that higher percentages of impervious cover result in higher stormwater runoff volume. Stormwater runoff contributes to flooding, erosion, and water pollution.

The City also uses standard hydrologic methods to design drainage improvements like storm sewers or creek bank stabilizations. These standard methods drive our construction costs and also closely relate to the observations from the 2008 Stormwater Runoff Study. Both standard methods and local observation indicate a strong correlation between runoff volume caused by development through the amount and the percentage of impervious cover.

Using both the percent and amount of impervious cover to calculate the charge provides a way to more closely relate the drainage charge to the individual impact of each property’s development to the operations and maintenance of the City’s drainage system.

The impervious cover data is generated using aerial photography collected every two years. Each pixel on the aerial photography represents 6 inches on the ground. The accuracy is suitable for defining the edges of buildings, patios, driveways and other types of impervious cover. This data was used to create impervious cover maps seen on the Find My Drainage Charge Map Tool. (For best results, use Internet Explorer 9 or higher, Firefox, Google Chrome or Safari.)

For properties developed or modified after the latest aerial photography, we use building permit data. Bills are typically adjusted based on the latest aerial photography in February during odd-numbered years.

If you make changes to impervious cover on your property, expect your drainage charge to change. However, there may be a lag time before changes are reflected in your charge. Changes that may affect your charge include increasing your parking, building an addition or adding a deck or shed. Removing impervious cover will reduce your charge. If you have removed impervious cover, please call 512-494-9400 to let us know, so we can adjust your charge for you sooner.

If you want an estimate of how changes to your property will affect your drainage charge, use the Drainage Charge Estimator.

The following information pertains specifically to the calculation and application of impervious cover for determining the drainage charge imposed by the City of Austin's Watershed Protection Department.

Impervious cover is any type of human-made surface that doesn’t absorb rainfall, including:

  • Rooftops
  • Patios
  • Driveways, paved and unpaved
  • Sidewalks
  • Roadways
  • Parking lots, paved and unpaved
  • Some decks

Uncovered wooden decks and unpaved portions of driveways count as 50% impervious cover. If you have these features, we may be able to lower the impervious cover on your account, which will in turn lower your bill. Please call 512-494-9400 and ask about an administrative review of your drainage charge.

A more complete definition of impervious cover is found in Section 25-8-63 of the Austin City Code. While impervious cover has broader implications in terms of urban planning and land development regulations, this information focuses on its connection to the drainage charge. For more comprehensive information about impervious cover regulations beyond the drainage charge, please refer to the appropriate resources and guidelines provided by the City's Development Services Department.


The impervious cover data was collected through aerial photography and LIDAR data that were converted into maps. In some cases, there may be areas that were incorrectly interpreted as either impervious or pervious cover. Please call 512-494-9400 if you think the impervious cover on your property needs to be corrected and request an administrative review.

Before you call there are a couple of things to keep in mind:

  • The City’s data on your impervious cover may not be the same as the appraisal district’s improvement values on your tax assessment. That is because the City includes driveways, walkways and other impervious areas not reported in the appraisal district data.
  • In some cases, the shaded impervious cover shown in the City’s “Find My Drainage Charge” map does not line up with the photograph beneath it. This is due to the aerial photography being taken at an angle, but it does not affect the amount of impervious cover. This is particularly likely to occur with tall buildings.
  • Aerial photography is precise to about six inches, sufficient for calculating the drainage charge. Keep in mind that one square foot of impervious cover is less than a penny a month.

For more information about how we collected the data and what is considered impervious cover, please see the other FAQs.

Information may not be available because the account holder has requested confidentiality. Under the Texas Utilities Code, customers have a right to confidentiality in government-operated utilities. A customer can request that their address, phone number, billing information and information related to their volume of utility usage be kept confidential. For more information, please visit the Austin Energy web page explaining Confidentiality and Customer Rights.

Alternatively, impervious cover may not be shown if the property was recently developed after the latest aerial photography was taken. The aerial photography was used to create the maps shown on the "Find My Drainage Charge" tool.