Assessing Your Homesite After a Wildfire


A wildfire sweeping across a homesite may cause damage even though the house survives. The intense heat, burning embers, and flames associated with such a fire may damage to various elements of the house.

Houses in a burnt forest

How does wildfire affect drinking and wastewater? 

Chemicals and Microorganisms

Chemicals and microorganisms are the primary source of contamination for drinking water after a wildfire because they can enter a firedamaged well. Human health could be adversely affected from either short- or long-term exposure to contaminants in the water. Sediment may cloud water or cause it to taste or smell smoky or earthy.  

Fire Retardants

Fire retardants can cause water to temporarily turn a reddish color. Fire retardants, made up of ammonium-based compounds containing phosphate or sulfate, are usually red in color due to a small percentage of iron oxide (Figure 1). Generally considered harmless to humans and land animals, fire retardants do have some level of toxicity to aquatic organisms. The most toxic component of a retardant product is the corrosion inhibitor.  

If a fire retardant was used near a wellhead, it could possibly seep into the well over time, particularly if the wellhead was damaged, or if it is in an area where storm water drains. In these situations, monitoring ammonia and nitrate concentrations for a period of several months is recommended. 

Assessing your drinking water and wastewater system after a wildfire 

Drinking Water

Complete a visual inspection of your private well system and then promptly repair any damage before use. The underground components of the well, pump, and septic system are often unharmed by wildfire. However, the wiring at the top of the well, the junction box, and PVC casing may be damaged.  

Damage to electrical wires, controls, pipes, tanks, and other components may affect system operation as well as compromise the safety of the water supply, or affect the proper disposal of wastewater. If the outside of your home or the yard area near your well has burned, you should have a licensed well technician inspect the system. Even if your pump is functioning burned wires not visible from the surface could result in problems with the pump. 

If you do not have power to your home following the fire, a generator can be used to run the well. l. Contact a licensed well contractor, electrician, or your power company to determine the proper generator size. Do not use an undersized generator because it can damage your pumping system. 

Once you have your well working, flush the system both inside and outside the house. If your water still tastes or smells earthy, smoky, or burnt, flush the water lines again and test the water with a certified laboratory for routine well water quality parameters, including metals. 


Onsite wastewater systems are more resistant to fire damage since most of their functional components are below ground. However, it is important to inspect your system for damage to PVC piping above or near the ground that may have been affected by heat. 

If your wastewater disposal system has been damaged, or if your system is backing up or malfunctioning, discontinue use and contact your local health department for guidance and instruction on repair and restoration of the system. 

Water treatment after a wildfire 

Testing Water

If a water test reveals that your drinking water has been compromised, the water should be treated before consumption. Metals, microorganisms, and other contaminants may be removed using the following methods: 

  • Well Disinfection – Private water wells can be disinfected through continuous chlorination or shock chlorination. 
  • Continuous Chlorination – A chemical feed pump is used to directly dispense chlorine into the well. 

Depending on the chlorine concentration, pH, and water temperature, the required contact time varies. For simple chlorination, the chlorine concentration is maintained at a low level of 0.2 ppm to 0.5 ppm with a minimum contact time of 30 minutes. In super chlorination, chlorine residues of 3 to 5 ppm are produced for approximately 5 minutes of contact time. 

Shock chlorination is the preferred method for disinfection of private water wells given its low cost, simplicity and effectiveness in most situations. This method of treatment is recommended for newly installed wells. It is a one-time treatment that is designed to kill bacteria in both the well and water system. The diameter of the well and the depth of water determine the amount of chlorine to be used for treating the well. The volume of water in the well can be determined using Table 1. Table 2. can be used to determine the amount of chlorine needed per 100 gallons of water in the well. An additional 100 gallons is added for the plumbing system 

Given the dangers posed by the use of chlorine gas for private well disinfection, most often liquid chlorine (sodium hypochlorite) or dry chlorine (calcium hypochlorite)is used. Sodium hypochlorite is the disinfectant in laundry bleach. 

Bleach loses its disinfecting capacity over time; therefore a fresh container of bleach should be used, free of fragrances and other additives. Electricity to the well should be turned off prior to starting the disinfection process. The exterior and accessible interior surfaces of the well should be scrubbed clean using a strong chlorine solution (1/2 gallon of chlorine laundry bleach per 5 gallons of water). This strong chlorine solution should be used to clean the well cap prior to removal. A 200 ppm solution of chlorine can be used in the well and plumbing system for at least 2 hours, but preferably overnight. 

Solutions above 200 ppm can cause the water to be too alkaline and reduce the effectiveness of the disinfection process. After removal and disinfection of the well cap, the diluted chlorine solution should be poured into the well. Water is then run back down the well for at least 15 to 20 minutes in order to recirculate the chlorinated water. The sides of the well casing and pitless adapter should be thoroughly rinsed during recirculation. 

Water disinfection filters and boiling

To disinfect by filtering, run your water through a two-micron filter (or smaller). Activated carbon, ultrafilters, or reverse osmosis filters can also be used. Cleaning the filter is essential to keep both a high rate of water filtration and bacteria from developing. 

To disinfect water by boiling, bring the water to a rolling boil for a least one minute. Boil longer at high attitudes or if the water is from a source suspected to have Giardia or other protozoa (five minutes boiling time is recommended at 10,000 feet above sea level). Boiling will kill microorganisms, though it will concentrate non-volatile chemical contaminants. Therefore, it is unwise to boil for longer than necessary. 

Allow the water to cool for at least 30 minutes before use. You can re-oxygenate the water by pouring the water back and forth between two clean containers to help improve its taste. 

How does wildfire impact other water resources? 

Impacts to Livestock Water

After a wildfire, ponds and streams are vulnerable to an influx of sediment, ash, fire retardant, nutrients, and other potential contaminants. 

Testing the water prior to turnout of livestock is recommended if you suspect the quality of your pond water has been impacted. Ash may contain trace levels of lead, antimony, arsenic, copper, mercury or zinc, but concentrations in water that exceed guidelines for livestock drinking water have rarely been documented.  

Indications that livestock have consumed poor quality water often include: 

  • Reduced food and water intake  
  • Changes in behavior and performance.  

If livestock appear to have signs of sickness, a veterinarian should be consulted, and an alternate water source should be used until their normal drinking source has been tested and treated. Assuming your pond is refreshed by clean stream water or groundwater, its quality should improve over time. However, if steps are not taken to prevent up-gradient erosion, the pond water can continue to deteriorate. 

Impacts to Fish and Wildlife

Large quantities of post-fire sediment and ash can overwhelm the habitat requirements for fish, as well as organisms that depend on water for some life stage, such as amphibians and insects. Although wildlife might be directly affected in the wake of a fire, they are not usually affected by water quality issues because of their ability to travel to new water sources. 

However, continued monitoring and inventory of fish and other aquatic organisms in a fire-impacted area is warranted. 

Impacts to Irrigation Water

Surface water that has deteriorated due to runoff from a fire is usually dark in color. It may have an increase in pH (will become more basic), total salt content, ash, and sediment concentration. 

A pH greater than 8.5 is considered high for irrigation water and can temporarily affect the availability of some plant nutrients and increase the sodium hazard if the water already has a high sodium adsorption ratio. 

In most cases, high concentrations of ash and sediment will be more of a physical problem with irrigation infrastructure and systems than a chemical hazard to crops. These components can clog filtration systems of sprinklers and drip systems, restrict head gates and diversion structures, and settle out in canals and ditches, reducing flow. 

Settling ponds and the addition of linear polyacrylamide may be one solution for reducing excessive sediment and ash if these are causing significant problems. In some cases, however, the increase in sediment may be beneficial as it can help seal leaky ditches and canals. 

Improving surface water quality after a wildfire  

Improvement Characterisitcs

Post-fire delivery of ash and sediment is the greatest concern for surface water health following a wildfire. High-alkalinity runoff from burned areas may increase surface water pH temporarily but tends to become neutralized as it is diluted by enough fresh water. Maximum impacts from ash and other fine-grained sediment tend to occur soon after the fire though may linger for several years.  

Ash input can contribute to increased nutrient levels as well; concentrations return to pre-fire conditions within several days to several months. To help improve surface water quality that could be adversely affected by post wildfire runoff, landowners can implement hill slope or channel treatment to trap sediment and prevent erosion (Figure 2). 

Hill slope treatment tends to be the most effective post-wildfire treatment; channel treatment is usually considered if hill slope treatment has proven ineffective. For the best location to install these treatments, landowners should assess the damage to their streams, ponds, and property. 

Damage will most often be visible in the form of increased erosion of upstream land or increased turbidity of the water body. If damage is not extensive, treatments may not be necessary, and natural processes will allow the area to return to its original state. 

Seeding, a common form of hill slope treatment, establishes barriers through plant growth. Seeding of a hill slope is often accompanied by an initial layer of mulch, certified weed-free straw, woodchips, or fertilizer.  

Other forms of hill slope treatment use physical barriers (i.e., logs, hay bales, sand or soil bags, fencing, trenches, and geotextiles) set perpendicular to the hill slope. Hill slope treatment also involves disturbing the ash, sediment, and soil to increase soil infiltration. Mechanical methods, such as a tractor pulling a harrow, are the usual means to increase soil infiltration. 

These practices can increase a potential supply of sediment unless the ground disturbance is followed by a substantial application of mulch, certified weed-free straw, or wood chips. In severe fires, the combustion of vegetative materials at the soil surface causes the soil to form a waxy layer that repels water, a phenomenon called hydrophobicity. This hydrophobic condition increases the rate of water runoff and can overwhelm water bodies in the event of thunderstorms. 

Channel treatment involves installing temporary, instream stabilizers and check dams with the goal of preventing high-speed runoff from downcutting the channel and eroding downstream riparian areas. Stabilizers slow the water in a stream by adding a physical barrier for the water to pass over; however, a stabilizer does not serve to trap sediment. Dams, on the other hand, collect sediment by detaining water for a period long enough for particles to settle out. Sediment, ash, and other material that has been deposited above a dam must be removed. Once debris transport and erosion are reduced, hill slope and channel treatments can be removed, and the ecosystem should be left to replenish itself. 

Author and Publication Date


By R. Waskom, J. Kallenberger, B. Grotz, and T. Bauder*  Date 8/2013 

Waskom, Colorado Water Institute, director; J. Kallenberger, research associate; B. Grotz, Colorado State University, department of civil and environmental engineering, student; T. Bauder, department of soil and crop sciences, water quality specialist.