Testing for free available chlorine in drinking water has never been easier

PATH and Precision Laboratories are pleased to announce the availability of an easy-to-use test strip to measure chlorine levels in drinking water. The test strip was designed to meet the needs of users in low-income settings who want assurance that chlorine dosage levels are optimal: sufficient to purify drinking water, but not so high as to negatively affect taste and odor.

The need for a new chlorine indicator test

Treatment with chlorine is well known as a cost-effective method of reducing diarrheal disease among low-income populations that lack reliable access to safe drinking water. One of the advantages of chlorine compared to other treatment options is that it provides protection from recontamination that can occur during transport and storage from a water source to the point of use.  In order to convey this important residual protection, the chlorine dosage needs to be accurate. Many chlorine-based treatment products in both liquid and tablet form come in one standard dose, making it difficult for users to know if the dosage is correct for their local water source and vessel size. All water sources vary in their need for treatment depending on both the source water itself and the season. In turbid water conditions, users are instructed to double the standard dose, but this can adversely affect the smell and taste of the treated water.

Local variation in water quality makes it important to periodically monitor chlorine-based treatment products and determine accurate dose size for local water sources and storage container sizes. Unfortunately, most chlorine indicator tests available in the market are either expensive, complicated, or both—making it difficult for people to use them consistently in developing country environments without specially trained personnel. Although some test strips are capable of reading free and total chlorine and multiple other parameters, users in our field trials indicated that the added time, complication, and cost of these features was not worth the benefit. What they wanted most of all was simplicity.

Developing the right product

With thirty years of experience developing appropriate technologies for developing country environments, PATH sought to develop a faster, cheaper, more accurate, user-friendly chlorine test. First, we defined the performance criteria for a chlorine indicator test that would be easy to use in developing country environments, then we rated existing chlorine indicator technologies, such as drops, tablets, test strips, and electronic systems like colorimeters, against those criteria. This process confirmed our initial assumption that a test strip would be the best technology platform to use. We then defined the key technology parameters, including the detection range, accuracy, precision, shelf life, and price that would be needed in a suitable product for low-income settings. In selecting a development partner, we identified and reached out to a range of companies already developing similar products. Precision Laboratories proved to be a good partner for PATH: not only did they have a good product and many years of experience; they also have a keen interest in the public health goal of reducing diarrheal disease by helping people gain access to safe drinking water.

The resulting drinking water test strip—now available through PATH—costs just $3.50 per bottle (100 strips), or $0.035 per test. The test is accurate to 0.01 parts per million (ppm) and detects free available chlorine at a range of 0-5 ppm in only five seconds.

The final test strip requires users to follow only three steps: (1) dip the strip in water, (2) move the strip back and forth for five seconds, and  (3) read the result. The indicator window shows whether free chlorine is below, within, or above our target range of 0.3 to 2.0 ppm. Initial feedback from users has been positive.

PATH’s plans for the test strip

PATH anticipates that the test strips will have an immediate market among organizations that treat drinking water with chlorine at the community level or that are involved in field research of chlorine-based treatment interventions, whether at the community or household level. These organizations typically monitor their treated water on a regular basis with costly and difficult-to-use indicator tests. With a more affordable and simple test strip, they can monitor water more frequently, using minimally trained staff.

The test strips can also be used by water kiosk entrepreneurs or community water committees to monitor chlorine-based treatment systems. For example, the test strips will be paired with a community-scale electrochlorination system from Cascade Designs, Inc., called the SE200. The SE200 uses water, table salt, and electricity from a 12-volt battery to produce a consistent concentration of chlorine that can be used to treat up to 200L of drinking water per 7-minute run cycle. By pairing the SE200 with chlorine test strips, operators of the SE200 have a simple tool to regularly and reliably monitor chlorine levels and avoid under- or over-treating drinking water.

Happier, healthier users

The Precision Laboratories test strips were designed to make it easy for unskilled users with little to no training to quickly and reliably determine whether chlorine residuals are in the safe range for drinking water (from 0.2 to 2.0 ppm). With this tool, users can be more precise with their dosing and ensure that the treated water is safe to drink and not overwhelmed with chlorine taste and odor. 

PATH is happy to provide a sample bottle to those interested in testing the new product. For more information, please contact ChlorineTest@path.org.

Illustration: PATH.