How reliable are water quality monitoring results from Field Test Kits

Water quality is an important factor in the provision of safe drinking water. Laboratory facilities for testing water quality are absent in most of rural India. Moreover, the collection, preservation and transportation of millions of samples from rural areas to regions with laboratory facilities is not feasible.

Field Test Kits (FTK) address this problem by acting as a screening and identifying platform for the sources which are at risk of contamination. FTKs provide a platform for participatory water quality monitoring, knowledge dissemination and awareness-raising. 

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However, the sensitivity of FTKs is questionable. Hence it is important to evaluate the reliability and sensitivity of FTKs in the desired concentration range.

FTKs are ranked based on their technical design, type of results, provision to remove interference, detection limit, the time required, ease of use (clarity of instruction manual and identification (colour compactor)), availability of consumables and cost of the kit.  

The sensitivity and specificity of kits contribute to the accuracy of results from the FTKs. The simple presence-absence tests for the detection of microbial contamination can be done using Clark’s Method.

But these tests are prone to numerous kit-based and user-based errors. FTKs are prone to false-positive test results due to interference from high sulphur content, Hydrogen sulfide (H2S) producing pathogens and chlorine-damaged pathogens.

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In samples containing non-H2S producing pathogens, high test variability with incubation time is observed. Due to low specificity or low detection limit, a high percentage of false-negative results are obtained.

User-based errors occur when proper instructions are not followed — conducting tests without washing hands properly, touching the interior of testing vials or sample bottles, shaking the vials inadequately after adding reagents or forgetting completely, inability to properly interpret the colour/result etc.

Demonstration on how to properly use FTKs and the instruction manual was found to reduce user-based errors in using FTKs.

Innovations in FTKs to detect and enumerate pathogenic organisms in drinking water based on highly specific methods like enzymatic chromogenic substrates improve the accuracy and reliability of FTKs.

FTKs integrated with smartphone-based colourimeters and mobile apps with an in-built Global Positioning System can reduce user-based interpretation errors.

It can provide rapid results and real-time monitoring/early warning. But advanced FTKs are expensive. While the initial equipment cost of such FTK is lower than the laboratory equipment, the consumable costs are high.

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The FTKs for the detection of chemical parameters generally include pH, temperature, conductivity, alkalinity, dissolved oxygen (DO), total hardness, nitrate, ammonia, chlorine, fluoride, iron, lead and arsenic.

Most of the FTKs, even cheaper ones, provide accurate and reliable results for relatively easily detectable parameters like pH, conductivity, DO, hardness and alkalinity.

However, the same FTK brands, when tested for nitrate and ammonia, provided inaccurate results. The FTKs that are used to detect lead, phosphate, arsenic (As) etc., provide accurate results for dissolved forms while the particulate fraction remains undetected.

Measures to convert particulate fraction (especially lead) after digestion using household-based acids (lemon juice and vinegar) are fairly successful but time-consuming (1-24 hours). In the case of FTKs for As detection, some kits do not detect As V or do not have provision to reduce As V to As III, leading to false-negative results.

The detection of chemical parameters especially As, fluoride and lead results in false negatives or lower values when there is interference from sulphide, iron, nitrate etc.

Low-cost kits are generally inaccurate, with a lot of false-positive and false-negative results. These kits do not detect the presence of contaminants if present in low concentrations hence resulting in false negatives.

The better performing kits providing accurate reproducible results are expensive. User-based errors in the interpretation of colour-chart-based results also lead to underestimation or overestimation of results.

Often sample colour interferes with test colour formation and also, there is a great difference in manufacturer-provided colour chart and field sample test colour, creating user-based errors.

Recent interventions include the use of smartphone-equipped FTKs with sensitive optical sensors to reduce user-based errors and interference reduction reagents to reduce kit-based errors at a low cost.

Some other challenges related to FTKs use are; Proper storage and inspection of kits.

The shelf lives of reagents are often one-two years and need to be kept away from moisture and direct sunlight.

Users are often less invested in following these instructions and replacement of reagents before expiration. All these factors also impact the quality of results provided by FTKs.

Availability of consumables is a challenge when using imported kits. This will delay the monitoring of water sources when there isn’t enough stock of reagents.

However, with proper training on the use and maintenance of FTKs, ensuring timely availability of consumables and regular quality checks on the FTK results, these kits can be a reliable means for water quality testing in rural areas.

The authors would like to acknowledge the financial support from the United States Agency for International Development (USAID). This review was conducted as a part of the REAL-Water project. The contents of this post are the sole responsibility of the REAL-Water consortium members and do not necessarily reflect the views of USAID or the United States Government

Views expressed are the authors’ own and don’t necessarily reflect those of Down To Earth

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