Drinking Water Quality Study of Tube Wells in Cambodia – Guidance Summary
August 1, 2008 Resource Development International Cambodia (RDI)
Thousands of wells are drilled in Cambodia each year, with the goal of supplying safe and accessible drinking water. The availability of clean drinking water is a basic right of all peoples. Unfortunately, many of these wells offer water which is either unsafe for human consumption and/or has such poor aesthetic quality that no one will consume it. Despite the potential magnitude of this problem, very little data has been gathered to prevent the senseless poisoning of villagers and the wasting of millions of dollars constructing wells that yield water of inferior quality.
In response to the need for an appropriate guidance tool, a drinking water quality guidence model and sampling program has been developed by RDI. Extensive tube well data collection activities have been performed in throughout the country. Thousands of tube wells have been tested and this number is growing daily. Each well has been tested for Arsenic, Manganese, Fluoride, Nitrate, Iron, Chloride, Hardness, Turbidity, pH, and Salinity and some wells for E.coli and total Coliforms. Using this data, guidance is provided and presented in three unique ways. First, a drinking water quality index (DWQI) has been calculated for each commune. A DWQI provides a simplified but powerful representation of the health and aesthetic conditions of drinking water within a spatial boundary. A health value represents the probability of encountering safe drinking water, and a letter grade reflects the potential acceptability of the water in terms of aesthetics (i.e. taste and appearance). Some communities learn to live with generally distasteful and displeasing water, but in some cases measures can be taken to improve its acceptability. Second, statistical analysis has been performed to determine the probability of each parameter exceeding its respective Cambodian water quality standard. Third, mapping tools have been utilized to present spatial interpretations of the data at both large and small scales. Sample locations are presented on large-scale commune maps, and samples that exhibit elevated concentrations of health-impacting contaminants are colour-coded appropriately. Small-scale province maps have been developed to provide insight into regional conditions and trends for each contaminant. These guidance tools are presented in provincial contaminant summary maps and commune groundwater quality analysis reports for the provinces selected for groundater characterization. The technical detail of the survey and its analysis have not been eliminated, but harnessed in such a way that it can be utilized as a simple, yet valuable decision-making tool.
Altogether, the guidance provided will allow end-users to make decisions that ensure funding is used appropriately and lives are not needlessly put at risk. Additionally, regions that already exhibit drinking water problems can be properly targeted and appropriate drinking water sources can be determined.
The following instructions are provided to assist with the analysis of the guidance provided in this report.
Drinking water quality guidance is provided in three forms: the DWQI, statistical analysis (probabilities), and spatial analysis. This section provides the information required to interpret these guidance tools accurately and effectively.
Applicability – The guidance in this study only applies to tube wells. Tube wells in Cambodia are typically drilled into aquifers at a depth of 20-90 meters, and are often fitted with a hand pump. Tube wells can provide consistent and safe drinking water where source aquifers are chemically safe. If placed in an inappropriate location, tube wells can provide unsafe or unacceptable drinking water. In such cases, alternative water sources could include rainwater, surface water (rivers, wetlands, or lakes), or shallow aquifer water (open/dug wells). It should be noted that shallow aquifer and surface waters are often contaminated with pathogens, but this is more easily removed (bio-sand, boiling, ceramic filter) than chemical contamination in the water.
Drinking Water Quality Index (DWQI) – A DWQI is calculated and presented for each commune in each analyzed province. It is a representation of the drinking water quality in the commune based on the parameters chosen for analysis (Arsenic, Manganese, Fluoride, Nitrate, Iron, Turbidity, Hardness, and Chloride). The index is broken up into a health value and an aesthetic letter grade. A health value represents the probability of encountering safe water in the commune, based on the samples collected. While no area can be assumed to be completely safe without proper water quality testing, the higher the DWQI is, the greater likelihood safe water will be encountered. The aesthetic letter grade (A to F) is a measure of the aesthetic quality observed. Most communes achieve very low aesthetic scores because there is little, if any, treatment of the water (i.e. filtration, chemical treatment). In some cases, the water may be unpleasant to drink, but this is difficult to quantify and individuals residing in a commune ranked with an ‘F’ may find their water to be acceptable. While most communes are represented by approximately 20 samples, DWQIs are reported for all communes where five or more samples were collected.
Probabilities – When a contaminant exceeds its respective drinking water standard in at least one sample in a commune, the contaminant is subsequently considered a ‘Contaminant of Potential Concern’. Contaminants of Potential Concern are presented in the commune reports, along with the corresponding probability of it being encountered above unsafe or unacceptable levels, based on the samples collected.
Spatial Analysis (Sample Locations) – In each commune report, the location of the samples collected are presented on a topographic commune map. It is important to understand that the DWQI and probabilities are based on data from the sample locations in the commune. It should also be noted that data may not have been collected in some portions of the commune, due to poor accessibility or the lack of wells in some areas. Thus, special consideration must be given if a well is to be placed in an area poorly represented by the sample locations. Special consideration must also be given when contaminations are restricted to localized portions of the commune, as the DWQI and probabilities represent all commune data collectively.
Spatial Analysis (Provincial Maps) – Provincial maps are presented outside of the commune reports. Small-scale maps have been created for the DWQI and tested contaminants, representing data for every commune in the provinces analyzed. These maps are useful in observing regional trends and defining areas of unsafe or poor groundwater conditions.
Altogether, these analyses provide an accurate, simplified, and powerful guidance tool. RDI intends to secure funding to complete similar analysis for the remaining provinces of Cambodia, as well as expanding it to include shallow aquifers and surface water.