Pet Waste and Water Quality

Pet waste is easy to dismiss as a nuisance rather than a pollutant — it is small, it is organic, and it seems like it should simply break down. In a watershed it does not behave that way. Dog waste is a concentrated source of fecal bacteria and nutrients that washes off lawns, sidewalks and trails into storm drains and, untreated, straight into the nearest stream. The pollution is well documented: genetic studies trace much of the fecal bacteria in urban runoff to non-human sources including dogs, and resident surveys show that even where people know the problem exists, a large share still do not clean up. This page lays out the water-quality pathway, the survey and loading numbers that quantify the problem, the practical solutions — pet-waste stations, digesters and disposal options — and the ordinance and outreach approaches that municipalities use to change behavior.

Why Pet Waste Is a Water Pollutant

The presence of pet waste in stormwater runoff has several implications for urban stream water quality, with the greatest impact coming from fecal bacteria. Dog feces also carry nutrients — nitrogen and phosphorus — that fuel weed and algae growth once they reach a lake or pond. It is the combination of pathogens and nutrients, not simple unsightliness, that makes pet waste a recognized nonpoint-source pollutant rather than a fertilizer.

The scale of the bacterial load is the part most people underestimate. A single gram of dog feces can contain about 23 million fecal coliform bacteria (van der Wel, 1995). Dogs are also significant hosts of Giardia and Salmonella (Pitt, 1998). When that material is left on the ground, the next rain carries the bacteria into the storm drain network, where — unlike sanitary sewage — it usually reaches receiving waters without any treatment.

How Pet Waste Reaches Waterways

The pathway is short and direct. Waste left on a lawn, sidewalk, trail or street is picked up by rainfall and snowmelt, carried as runoff across impervious surfaces, and routed into a storm drain. In most urban drainage systems the storm drain discharges to the nearest stream, river or bay with no treatment step in between. That is the crucial difference between pet waste and the waste handled by sanitary sewers: storm drains are designed to move water quickly, not to clean it.

Because the connection is so direct, waste deposited near a buffer, ditch or drainage way is the most damaging — it is hydraulically connected to the stream and reaches it with the next storm. Waste decaying in the open also releases its nutrients into runoff. The release of nutrients from decaying pet waste promotes weed and algae growth in lakes and ponds, which limits light penetration, suppresses aquatic vegetation, and can lower dissolved-oxygen levels enough to affect fish and other aquatic organisms — the process of eutrophication. The same storm-drain-to-stream link is why catch-basin maintenance and broader residential stewardship practices matter for bacterial pollution control.

The Numbers: Pet Waste Pollution Statistics

Several lines of evidence quantify how much pet waste contributes to bacterial pollution. Genetic and bacterial-source-tracking studies by Alderiso et al. (1996) and Trial et al. (1993) both concluded that about 95 percent of the fecal coliform found in urban stormwater was of non-human origin. A bacterial-source-tracking study in a watershed in the Seattle, Washington area found that nearly 20 percent of the bacteria isolates that could be matched with a host animal were matched with dogs. A 1982 study of Baltimore, Maryland catchments found that dog feces were the single greatest contributor of fecal coliform and fecal strep bacteria (Lim and Olivieri, 1982).

The loading can be enough to close a waterbody to recreation. It has been estimated that for watersheds of up to twenty square miles draining to small coastal bays, two to three days of droppings from a population of about 100 dogs would contribute enough bacteria and nutrients to temporarily close a bay to swimming and shellfishing (US EPA, 1993). At a larger scale, in the Four Mile Run watershed in Northern Virginia a dog population of about 11,400 is estimated to contribute roughly 5,000 pounds of solid waste every day and has been identified as a major bacterial contributor; of approximately 500 fecal coliform samples taken from the stream and its tributaries since 1990, about 50 percent exceeded Virginia water quality standards for fecal coliform bacteria (NVPDC, 1998).

Survey Data: What Residents Actually Do

Whether pet waste becomes a pollutant depends on behavior, and several resident surveys have measured that behavior directly. In a survey of Chesapeake Bay residents, about 41 percent of households owned a dog; just under half of those owners actually walked their dog in public areas, and of the dog walkers, about 59 percent cleaned up most or all of the time (Swann, 1999). Men were found to be less likely than women to pick up after their dog. These figures are broadly consistent with other surveys, summarized below.

The surveys reveal a consistent split: a strong majority agree that dog waste can be a water-quality problem (Hardwick, 1997; Swann, 1999), yet residents generally rank it as the least important local water-quality problem (Syferd, 1995; MCSR, 1997). That gap between awareness and priority is the central challenge for any pet-waste program — people know, but do not act on what they know.

The reasons owners give for not picking up are revealing, and the reluctance to handle dog waste is the single biggest limitation to controlling it. Recorded rationales (HGIC, 1996) range from “because it eventually goes away” and “too much work” to “it’s on the edge of my property,” “it’s in the woods,” “small dog, small waste,” and “use as fertilizer.” The reasons given for picking up are more straightforward: it’s the law, environmental reasons, hygiene and health, neighborhood courtesy, and keeping the yard clean.

Estimating the Load From Pet Waste

Translating a dog population into a bacterial or nutrient load follows the same approach used for any nonpoint source: count the source, apply a per-unit loading rate, and route it through the catchment. The Four Mile Run figures show the method in outline — a population of about 11,400 dogs producing roughly 5,000 pounds of solid waste per day — while the per-gram bacterial count (about 23 million fecal coliform per gram) converts mass into an organism count.

To estimate the runoff and pollutant load that carries that material from a specific catchment — using local rainfall, impervious cover and event mean concentrations — use the Simple Method runoff and pollutant-load calculator. For the corresponding removal performance of downstream practices, the bacteria figures in the pollutant removal database show how much treatment a given practice can be expected to provide.

Best Management Practices for Pet Waste

Animal-waste collection as a source control combines educational outreach with enforcement to encourage residents to clean up after their pets. No engineered practice removes pet-waste pollution as effectively as preventing the deposit in the first place, so the core management practices target behavior: awareness campaigns, signage, convenient disposal infrastructure, and pet-waste control ordinances. Public education programs often fold the pet-waste message into a broader nonpoint-source message, using brochures and public-service announcements to create an explicit link in residents’ minds between pet waste, the storm drain, and local water quality.

Because the pollutant removal abilities of pet-waste collection programs have never been precisely quantified, programs are evaluated on participation and behavior change rather than on a measured percent-removal figure. There is ample evidence that such programs are necessary in urban areas, and the practical levers are well established: make cleanup easy (stations and bags), make it expected (signage and ordinances), and make it understood (outreach connecting waste to water). Related residential practices — including lawn and landscaping care — reinforce the same nutrient-and-bacteria message.

Pet Waste Disposal Solutions

The infrastructure that makes cleanup convenient is the visible half of a pet-waste program. Several options are used alone or in combination, sited and designed to minimize their own stormwater impact.

Pet waste stations and bag dispensers

A pet-waste station combines a bag dispenser, a covered waste receptacle and a reminder sign in one unit, placed where dogs are walked — park entrances, trailheads, apartment commons and along popular routes. Stations work as on-site reminders as much as disposal points: signs in public parks and the provision of receptacles for pet waste both encourage cleanup by removing the two common excuses, not being prepared and having nowhere to put it. Siting matters — stations should be placed where foot traffic is highest and kept out of drainage ways — and the receptacles need a regular emptying schedule to stay effective. Signs may cost more up front than printed materials but last for years and act as continuous on-site reminders.

In-ground digesters

An in-ground pet-waste digester is a unit installed below grade into which collected waste is deposited; decomposition occurs within the unit, so there is no refuse to collect. The Australian “doggy loo” is the same idea — an in-ground disposal unit where waste breaks down in place with minimal maintenance. Digesters suit single yards, dog parks and small common areas where a regular trash-collection route is impractical, and they keep the waste out of the surface drainage path entirely.

Disposal methods: trash, toilet and compost

Surveys show residents already use a mix of disposal methods. Bagging and placing waste in the trash is the most common (54–66 percent across surveys), flushing to the sanitary sewer via the toilet is next (12–20 percent), and a small share compost it (about 4 percent). Flushing routes the waste to sanitary treatment rather than the storm drain; trash disposal routes it to a landfill. Each keeps the waste off the ground and out of runoff, which is the objective. Biodegradable bags help with landfill impact but do not change the water-quality calculus on their own — the water-quality benefit comes from the waste being collected, not from the bag material.

Designated dog parks

In some areas, parks or portions of parks established specifically for dog owners have gained popularity. With provisions for proper disposal of feces and with siting and design that address stormwater runoff, these parks can be an option for protecting local water quality. Management approaches documented in Australian dog parks include the pooch patch — a designated post surrounded by sand that owners introduce their dog to on entry, with bins provided nearby — and the “long-grass principle,” in which areas mowed less frequently (grass around 10 cm) are provided for feces to disintegrate naturally away from drainage. The design of dog parks should mitigate stormwater impacts through vegetated buffers, pooper-scooper stations, and siting out of drainage ways, streams and steep slopes.

For Municipalities: Ordinances, Signage and Outreach

Programs to control pet waste typically rely on “pooper-scooper” ordinances. These require the removal and proper disposal of pet waste from public areas and others’ property before the owner leaves the immediate area, usually with a fine attached to encourage compliance. Some ordinances go further and require owners to remove waste from their own property within a set time frame. Model ordinance language and the broader regulatory framework are covered in the stormwater management ordinance material, and the storm-drain connection that makes pet waste a regulated discharge is addressed under illicit discharge and connection controls.

Enforcement alone has limits. According to the Chesapeake Bay survey, 44 percent of dog walkers who do not pick up indicated they would still refuse to do so even if confronted by neighbors’ complaints, threatened with fines, or offered more sanitary and convenient retrieval and disposal options. That hard core of non-compliance suggests an alternative message is needed alongside the ordinance: encouraging rudimentary manure management by training dogs to use areas that are not hydraulically connected to the stream or close to a buffer. The most effective municipal programs combine all of the levers — an ordinance with credible enforcement, well-maintained stations and signage as on-site reminders, and sustained outreach that links pet waste to local water quality — rather than relying on any single tool. Costs vary with the intensity of the effort: ordinance programs must budget for enforcement staff and equipment, while education costs depend on the materials and distribution chosen.

What Works: The Evidence

The honest position is that pet-waste programs are evaluated on necessity and behavior rather than on a measured removal rate, because the pollutant-removal ability of collection programs has never been quantified. What the evidence does establish is that pets and urban wildlife can be significant bacterial sources — from the per-gram coliform counts to the source-tracking studies pointing to dogs — and therefore that enforcement and education to raise resident awareness are warranted. The strong resistance some owners show to handling waste means the highest-return investments are usually the ones that lower the effort and raise the social expectation simultaneously: convenient, well-stocked stations paired with clear signage and a consistent outreach message connecting the waste on the ground to the water downstream.

References

• Alderiso, K., D. Wait and M. Sobsey. 1996. Detection and Characterization of Male-Specific RNA Coliphages in a New York City Reservoir to Distinguish Between Human and Non-human Sources of Contamination. American Water Resources Association, Herndon, VA.
• Hardwick, N. 1997. Lake Sammamish Watershed Water Quality Survey. King County Water and Land Resources Division, Seattle, WA.
• Home and Garden Information Center (HGIC). 1996. Residential Fertilizer Use Survey. University of Maryland Cooperative Extension, College Park, MD.
• Lim, S. and V. Olivieri. 1982. Sources of Microorganisms in Urban Runoff. Johns Hopkins School of Public Health and Hygiene, Baltimore, MD.
• Minnesota Center for Survey Research (MCSR). 1997. Lawn Care Survey — Results and Technical Report. University of Minnesota, Minneapolis, MN.
• Northern Virginia Planning District Commission (NVPDC). 1998. Four Mile Run.
• Pitt, R. 1998. Epidemiology and Stormwater Management. In Stormwater Quality Management.
• Swann, C. 1999. A Survey of Residential Nutrient Behaviors in the Chesapeake Bay. Center for Watershed Protection, Ellicott City, MD.
• Syferd, E. 1995. Water Quality Consortium Research Summary Report. Seattle, WA.
• Trial, W. et al. 1993. Bacterial Source Tracking: Studies in an Urban Seattle Watershed. Puget Sound Notes 30:1–3.
• United States Environmental Protection Agency (US EPA). 1993. Guidance Specifying Management Measures for Sources of Nonpoint Pollution in Coastal Waters. Office of Water, Washington, DC.
• van der Wel, B. 1995. Dog Pollution. The Magazine of the Hydrological Society of South Australia 2(1):1.

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