How can water risk assessments build redundancy in your water supply?
June 11, 2025
Water systems usually have backups. But the water sources themselves often get less attention¡ªuntil trouble arises. Water risk assessments can help.
In general, most people expect their water supply to be safe and available. They expect clean water every day. This is especially true in places with ample rain. Water systems usually have backup pumps, treatment units, and power sources.
But the water sources themselves often get less attention¡ªuntil trouble arises.
There was a widespread loss of water service that impacted our Richmond, Virginia, area offices in January 2025. More than a million people lost access to clean water for five days. Why? It was a combination of weather, electrical, and mechanical factors. In addition to the city itself, Richmond is a major supplier of water to nearby communities. This crisis has started local discussions about water risk assessments and why water supply redundancy is important.
Many communities depend on a single water source. A major example is the US Capital Region. Millions of people in Washington, DC, Northern Virginia, and Maryland rely solely on the Potomac River for their water. Seeing this weak spot, the U.S. Army Corps of Engineers received $3 million in funding in October 2024 to conduct a Backup Water Supply Feasibility Study for the region.?
Repurposing quarries can provide new water sources and increase water storage capacity. The Belwood Quarry now provides 2.4 billion gallons of water storage for Atlanta, Georgia.
Of course, the DC area is very visible. Many smaller water systems also lack redundancy but tend to receive less attention.
Why aren¡¯t redundant water sources more common? Sometimes, no other water source is available. More often, cost is the issue. Budgets focus on urgent needs, and resilience planning is delayed. Using multiple water sources also adds complexity and costs, both up front and ongoing.
America¡¯s Water Infrastructure Act requires utilities to update Risk and Resilience Assessments in 2025 or 2026. The deadline depends on the size of the population served. So, this is an ideal time to conduct a source water risk assessment and develop mitigation strategies. When possible, these strategies should include an assessment of source water redundancy. Here we will discuss many of the threats facing water supplies and options for utilities looking for ways to reduce risk.
Threats to water sources
Losing a water source can be an economic and human health disaster. Careful planning for source water protection can reduce risks, but no system is fully safe. All water sources are vulnerable to impacts from diverse natural and man-made hazards. These include extreme weather, contamination, and competition for resources. Let¡¯s look at each of those.
Threat #1: Extreme weather
Drought is an obvious natural threat to our water supply. Groundwater and surface water sources that receive direct recharge from rain or snowmelt are the most vulnerable. These water sources include rivers, reservoirs, shallow unconfined aquifers, and some fractured-bedrock aquifers. Even deep wells in confined aquifers can be affected since irrigation needs rise in dry periods.
Governing limits may come into play before the amount of water is physically reduced. For example, many surface water permits limit withdrawals to a certain percentage of total flow. Water quality can also decline during drought due to higher concentrations of contaminants because there is less dilution.
In addition to providing hydroelectric power, Douglas Lake supplies water to the City of Pigeon Forge, Tennessee.
Too much water can also be a problem. Floods can introduce contaminants from sewers, chemicals, and runoff. This mostly affects surface water but can also reach groundwater through flooded wellheads or aquifers near the land surface. The impact from floods is typically temporary. It is resolved when the water recedes. In extreme events, however, water sources can be taken out of commission for longer periods of time.
For example, in 2024, Hurricane Helene altered river channels and caused landslides in the Southeastern US. These caused enough erosion to make some water sources too turbid for use without extensive treatment months after the storm.
Threat #2: Contamination
Direct chemical spills, or floods as noted above, can taint water sources. Small spills occur often, especially in large river systems, but major events can overwhelm treatment plants. Spills or floods that reach groundwater sources often have longer-lasting impacts due to the slow movement of groundwater. Other threats to water quality include:
- Nonpoint source pollution: The concentrations of contaminants can gradually build from poor farming practices, faulty septic systems, and urban development.
- Emerging contaminants: Substances like PFAS may already be present. Often, they go undetected until regulations change.
- Natural contaminants: Increases in pumping rates or times can draw in poorer-quality water from different areas.
This is an ideal time to conduct a source water risk assessment and develop mitigation strategies. When possible, these strategies should include an assessment of source water redundancy.
Threat #3: Competition for water
Competition for water resources can look a bit different from place to place depending on water law, but the premise is the same. Water resources do not abide by property lines, and one use can impact another. Growing populations and industries increase pressure on limited resources.
In 2025, the U.S. Geological Survey identified nearly 30 million people who live in parts of the country where surface water supplies were limited or insufficient. When demand is too high, water systems must conserve, limit development, or find new sources. But conservation efforts only go so far. And limiting development is rarely a popular decision.
This is a widespread issue. California¡¯s groundwater crisis. Legal fights over the Colorado River. And depleted aquifers in the Midwest and East Coast of the US are just a few examples.
In many places, getting permits for new water use is now very difficult. In Virginia, our hydrogeologists spend much of their time developing and permitting groundwater resources. Virginia usually has ample surface water but many parts of the state are far from sizeable surface water sources or treatment is cost prohibitive. As a result, aquifer systems are overdrawn. Now, permitting groundwater withdrawals can be difficult, and what¡¯s really needed are detailed studies of potential alternatives. We are currently helping clients investigate alternate water sources to reduce reliance on the Potomac aquifer. This has historically been the most certain source of groundwater for much of Virginia.
Competition can also occur on a more local scale. For example, large groundwater withdrawals can lower water levels in other nearby wells, which limits their ability to pump as much water. This is especially true in fractured bedrock aquifers, where seemingly small withdrawals can cause large declines in water levels at great distances.
What does water redundancy look like?
The best source of redundancy depends on the risks a system faces. For drought, adding a river intake in the same watershed may not help. But for contamination or competition, it could be a good solution. A water risk assessment can help support this decision.
When possible, a different type of source water can provide the best security. For example, a drought may not impact a deep confined aquifer system. Common options include new wells, river intakes, reservoirs, and interconnection to another water system (assuming that system has a different source water). There are other options to consider. They include aquifer storage and recovery, stormwater capture, wastewater reuse, and desalination.
Testing of this new groundwater supply well in Fauquier County, Virginia, included pumping at a constant rate for three days while monitoring water levels and water quality data.
Ideally, complete redundancy is provided by an alternate water source capable of meeting all of a water system¡¯s demand. But there are benefits of having the capacity to meet even just a portion of the demand. This can provide a temporary supply or be blended with the primary source water for supplemental capacity or improved water quality. A perfect example of this is the Town of Purcellville, Virginia.
The town provides clean water to about 9,000 residents. It has a well-structured combination of groundwater wells and a spring-fed reservoir. This system promotes resilience, as the town benefits from a degree of redundancy. During drought periods, the wells, which typically experience a smaller decline in yield compared to the spring, help maintain a consistent water supply.
In 2022, trace amounts of PFAS chemicals were identified in several of Purcellville¡¯s wells. We worked with the Town to develop an innovative water-blending strategy. This proactive approach greatly reduced the amount of PFAS in the water delivered to residents. The success of this strategy underscores the importance of the town¡¯s diverse water sources, including wells in other parts of Purcellville that were free from detectable PFAS.
If you manage a utility or commercial water system, consider ways to increase redundancy in your next water risk assessment. Developing new sources can be complex and costly. But so is the unexpected loss of water. Funding assistance is often available, especially for small and underserved communities.
