What Is Faecal Source Tracking, and Why Does it Matter for Water Management?

A beach closure tells you something is going wrong.

Sometimes this closure is due to positive test results for E. coli or Enterococcus spp. and sometimes it is due to predictive modelling because it happens frequently under similar environmental conditions.

These responses do not address the most important questions:

Where is the contamination coming from and what can be done to prevent it?

Faecal source tracking (FST) is the process of identifying the origin of faecal contamination in a water body - specifically, whether it comes from human or non-human sources. For the teams responsible for managing recreational waterways, stormwater systems, and catchment health, that distinction has direct operational consequences.

Until recently, answering it required laboratory analysis, time delays of at least 24-72 hours, and specialist expertise. Rapid molecular testing has changed that. The ZiP-P2 platform can now deliver a human-specific faecal contamination result in the field, in under 20 minutes, from a single water sample.

The Difference Between Faecal Indicator Bacteria and Faecal Source Tracking

Standard water quality testing relies on faecal indicator bacteria (FIB), primarily Escherichia coli (E. coli) and Enterococcus spp. These organisms live in the intestines of both humans and animals. Their presence in water signals recent faecal contamination. They are well-validated, widely used, and internationally accepted as microbial markers of water quality and are extrapolated as markers of health risk. Traditionally they are detected and quantified by transporting water samples to a laboratory for microbiological culture which takes at least 24-72 hours.

The use of these traditional testing methods is also limited by lack of specificity. E. coli and Enterococcus spp. can come from humans or a range of other animals. Their presence cannot tell you whether the source of contamination is a leaking sewer, a malfunctioning septic tank, wildlife at the water's edge, or livestock in the catchment. Each of those situations calls for a different management response.

Faecal source tracking (FST), also referred to as microbial source tracking (MST), tests for specific genetic markers that can indicate the likely animal source. To identifying human faecal contamination, the most reliable marker currently available is Bacteroides dorei, specifically, its HF183 genetic sequence.

Why Bacteroides dorei is the key marker for human faecal contamination

Bacteroides dorei is an obligate anaerobe that lives predominantly in the human gastrointestinal tract. It does not survive well outside the human body and is largely absent from the gut microbiome of most other animals. When the HF183 genetic marker is detected in water, it provides strong evidence of human faecal contamination from sewage infrastructure, septic systems, or direct human input.

This specificity is what makes Bacteroides dorei testing so operationally useful. It confirms that faecal contamination is present and narrows the investigation to human sources. This enables precise targetting of resources towards the most likely source.

The ZiP-Bactx-P2 field-based test targets the Bacteroides HF183 16S rRNA genetic marker. Semi-quantitative results are delivered in only 10–20 minutes and have a limit of detection of 125 copies per assay.

How Faecal Source Tracking Works in Practice

Running a faecal source tracking investigation with the ZiP-P2 platform does not require a laboratory or specialist environmental microbiology training. The workflow is designed for field teams operating in coastal, riverine, and urban stormwater environments.

Sample collection

Water samples are collected directly from the target site - beach locations, stormwater outfalls, groundwater seepage points, or rivulet monitoring stations. The ZiP Water Accessory Kit provides all the collection materials required. Test kits are suitable for ambient-temperature transport, with no cold chain required.

Testing in the field

The ZiP-Bactx-P2 test cartridge contains lyophilised (freeze-dried) assay beads. The four-step guided workflow takes under three minutes of hands-on time: add the sample, dilute with the provided buffer, load the cartridge, and start the run on the ZiP-P2 instrument. The instrument manages the amplification process automatically, with on-screen guidance throughout. There is no test result interpreation required. A semi-quantitative test result is provided to indicate the level of contamination (negative, low positive, mid positive or high positive).

The ZiP-P2 processes up to two samples simultaneously, supports continuous random access, and includes a range of integrated quality controls (instrument self-tests, test internal controls and external control material verification) to ensure result confidence in field conditions. With results available in less than 20 minutes, you've just saved a time-delay of 24-72 hours. You are also in the key location where direct management decisions can be implemented immediately and driven by real-time data. This prevents avoidable heath risks.

Results can be tagged with GPS coordinates, time-stamped at point of collection, and uploaded to central databases or geospatial mapping platforms. This enables real-time spatial tracking of contamination across a monitoring network, a capability that delayed lab-based culture testing cannot provide.

Why This Changes the Management Response

The management implications of knowing the source of faecal contamination are substantial. E. coli or Enterococcus spp. above a threshold in recreational water triggers a precautionary response - often closure of the site. That closure continues until repeat testing confirms the water is safe. This may also be delayed if relying on lab-based testing. Without faecal source tracking data, the problem just continues and the health risk is perpetuated.

When field teams know that elevated E. coli or Enterococcus spp. levels are accompanied by a positive Bacteroides dorei result, the investigation changes. The contamination is human in origin, and the likely entry points are likely to be from sewage infrastructure, ageing septic systems, or stormwater sewer cross-connections. That data reduces investigation time and directs remediation efforts precisely.

Conversely, when E. coli or Enterococcus spp. levels are elevated but Bacteroides dorei is absent, the contamination profile is more likely to be from non-human sources like wildlife, birds, dogs, or livestock in the catchment. This context supports more proportionate responses and reduces the risk of unnecessary or extended closures.

Real-World Results: Derwent Estuary Program Case Study

The Derwent Estuary Program (DEP), a collaboration between the Tasmanian Department of Health, EPA Tasmania, and the six councils bordering the Derwent Estuary, has conducted field investigations using the ZiP-P2 platform and the ZiP-Bactx-P2 test. The results demonstrate what faecal source tracking delivers in practice.

What Faecal Source Tracking Does Not Replace

Bacteroides dorei testing is a source investigation tool. It is not a replacement for general faecal indicator monitoring programs. E. coli and Enterococcus spp. testing remains the established method for routine water quality assessment, and the validated basis for management decisions about recreational water safety.

Bacteroides dorei testing adds value is in targeted investigations: when general indicators have flagged elevated contamination and the source is unknown; when stormwater system investigations need to distinguish human from non-human faecal contamination; or when councils and catchment managers need to prioritise remediation across multiple sites.

Used as a complement to existing programs, faecal source tracking with the ZiP-P2 platform extends what field teams can learn from a single site visit, without adding laboratory processing time or specialist expertise requirements.

Who Uses Faecal Source Tracking and When

Faecal source tracking is relevant wherever the origin of faecal contamination matters for the management response. Based on deployments of the ZiP-Bactx-P2 test, the most common use cases include:

• Stormwater and rivulet monitoring programs investigating suspected sewer cross-connections or aging infrastructure

• Beach Watch investigations where elevated traditional indicators are of uncertain origin

• Septic tank impact assessments in coastal and semi-rural areas

• Catchment health programs tracking human faecal inputs across multiple sites over time

• Emergency contamination response, where rapid source identification supports faster, more targeted intervention

The ZiP-Bactx-P2 test is intended for use by environmental health officers, community groups, water authorities, and field response teams. The platform requires no cold chain for storage or transport, operates on battery power in the field, and delivers results within 20 minutes of sample collection. Learn more at zipdiag.com/product-page/zip-bactx-p2 and zipdiag.com/water-testing.