Water Supply Watershed Protection Program


Frequently Asked Questions


Is my property located in a water supply watershed?

All land is located within a watershed of one kind or another, but only 20% of North Carolina's land area is classified as being within water supply watersheds.  Check with your local government to see if the watershed rules are in effect in your area.  If they are, the local government will have a map showing the boundaries of the watershed(s).  NCOneMap or the Stormwater Program Interactive Map Viewer may be able to show you if you are in or out as well.  If you have further questions, contact us


Will this program stop development?

No!  The only classification which prohibits new development (WS-I) contains no privately-owned land.  For other classifications, using density bonuses, density averaging or other flexibility measures built into the rules gives communities and developers ample possibilities for growth.  Refer to the water supply watershed classification table for details.  


What is "built-upon area"?  How do I calculate it?

Built-upon area is a measure of the hard surfaces or impervious cover for a site.  For each piece of land, divide the amount (area) of impervious surface (e.g., structures, roads, parking lots) located on site by the total land area under consideration.  Multiply the resulting fraction by 100 to get the percent built-upon area.  Refer to Streamlines Vol. 1, no. 5 for more information regarding impervious surfaces. 

What is the "critical area"?

Critical area is the land adjacent to a water supply intake where risk associated with pollution is greater than from remaining portions of the watershed.  Critical area is defined as land within one-half mile upstream and draining to a river intake or within one-half mile and draining to the normal pool elevation of water supply reservoirs.  Critical areas are more restrictive than areas outside this area.

What is the "protected area"?

Protected areas are only located within WS-IV watersheds.  A protected area is defined as land within five miles and draining to the normal pool elevation of water supplies/reservoirs or within ten miles upstream and draining to a river intake.

What is the purpose of a "buffer"?

The purpose of a buffer is to provide a vegetated area along streams through which stormwater runoff can flow in a diffuse manner, infiltrate into the soil, and allow filtration of pollutants.  There are two types of buffer requirements:  an agricultural buffer and a development buffer.  For agriculture, the buffer is only required in the critical area and is measured from the stream bank landward for a distance of ten feet.  For development activities throughout the watershed, buffers are required along all perennial waters with a minimum width of 30 feet for low-density development and a minimum 100-foot for high-density development (this includes use of the 10/70).  The buffer is measured perpendicularly from the streambank (or from the normal pool elevation of reservoirs) and serves as a setback for new structures such as houses, barns, and other buildings.  Property owners are encouraged, but not required, to maintain at least the first 25 feet of the buffer next to the stream in a naturally vegetated or undisturbed state.  Property owners and land developers are recommended to leave the buffer areas in public ownership and/or to dedicate them as a linear greenway or park.  For more information on how buffers can help water quality, refer to Streamlines Vol.1, no. 4.

What is the "10/70 provision"?  How does it work?

With the 10/70 provision, a local government can use 10% of the non-critical area of each watershed wtihin its jurisdiction for new development and expansions to existing development up to a 70% built-upon area limit -- without stormwater control -- if using the low-density option throughout the remainder of the watershed.  The 10/70 provision is available within WS-II, WS-III, and those WS-IV water supplies where the local government allows only development using the low-density option.  Please note that local governments can use this technique to "swap" publicly-owned, flood prone, or otherwise undevelopable land in order to target growth at a higher density elsewhere within the watershed.  The 10/70 provision is considered a "high density" option and therefore requires a 100-foot buffer along all perennial streams when being utilized.

What is the difference between the low- and high-density options?

The high-density development option allows for more built-upon area on a site through the use of stormwater management techniques to mitigate the effects of the increased impervious surface and the resulting increased rainfall runoff.  Depending upon the watershed classification, low-density development may allow up to 2 dwelling units per acre (24% built-upon area).  With the high-density option, development can potentially reach a 70% maximum built-upon area, depending upon the watershed classification.  For a detailed discussion about using the high-density option, refer to Streamlines Vol. 1, no. 3.  The water supply watershed classification table has more details regarding low- and high-density built-upon area limits for the various watershed classifications.

What are Best Management Practices (BMPs)?

BMPs are structural or non-structural management-based measures used singularly or in combination to reduce nonpoint source inputs to receiving waters in order to achieve water quality protection goals.  Streamlines Vol. 1, no. 2 contains more information regarding alternative stormwater management techniques.  See the NC Stormwater Best Management Practices Manual.


Do you have a question about the water supply program that is not answered here?  Send our Unit Staff an email message with your question.  We'll answer it as soon as possible.