Assessment of groundwater quality in shallow wells within the southern districts of Malawi

Abstract

Lack of safe drinking water is a major problem in developing countries. Within Africa most people rely mainly on local groundwater sources for their water needs. These can be deep boreholes or shallow wells, the latter are normally found in poorer communities as they are the least expensive to construct. Over time water from these sources can be contaminated leading to fatal consequences. Previous monitoring of the quality of water from boreholes and shallow wells have been irregular, with the focus being mainly on boreholes. Information on seasonal water quality changes in shallow wells used by rural communities in Malawi has generally been lacking.

A study was conducted from 2006 to 2007 to determine the quality of water from shallow wells in three districts in southern Malawi namely, Balaka, Chikwawa and Zomba districts. Water samples from 21 covered and five open shallow wells were analysed for chemical, microbiological and physical parameters using a portable water testing kit. Sampling was carried out at four different times of the year i.e. in August and October 2006 (dry season) and February and April 2007 (wet season). Microbiological data indicated that around 80% of the samples, obtained from the covered wells, failed to meet safe drinking water limits, set by World Health Organisation guidelines and Malawi Bureau of Standards, of zero total and faecal colony forming units (cfu)/100 ml. Values in excess of 1000 cfu/100 ml were noted in 10% of the samples, indicating gross contamination and the probability of pathogens being present. Contamination levels were higher during the wet season than the dry season in all three districts. Arsenic, ammonia, nitrate, nitrite and sulphate were all within the acceptable limits. Elevated levels of hardness, turbidity were noted in certain wells.

Introduction

Water-related diseases are responsible for 80% of all illnesses/deaths in developing countries, and kill more than 5 million people every year (UNESCO, 2007). In Malawi, only 65% of the population have access to safe drinking water and 50% of all illnesses are solely due to water-related diseases (Kalua and Chipeta, 2005). Water is a medium of thousands of microorganisms some of which are disease causing. Diseases in humans can be caused by the presence of certain pathogenic bacteria and other organisms such as viruses, protozoa and worms. Pathogens, causing diarrhoea-related illness such as cholera, are commonly derived from human faecal material. The mortality rate in Malawi in 2002 from cholera was over 50% of the water-related deaths. During the 2001/2002 rainy season, 33,150 cholera cases and 980 deaths were recorded in Malawi (Davis, 2005). Globally, 4 billion cases of diarrhoea are reported every year causing 1.8 million deaths, out of which about 90% are children under five (UNESCO, 2007). Pathogens can readily be washed into water bodies such as shallow wells. Without treatment, such water is a major cause of illness if consumed and may result in loss of productivity and increased medical costs. Potable water is defined as water that is free from pathogens, low in compounds that are acutely toxic or that have grave long-term effects on human health (Shultz and Okun, 1984). Potable water should also be free from compounds that can cause colour, taste (high salinity) and odour.

Shallow wells (Fig. 1) are normally located in the valleys where the groundwater table is relatively high (1–4 m below ground level) and infiltration of rain and river water plays a main part in groundwater recharge. Boreholes however draw water from deep (20–80 m or more) aquifers. In Malawi alluvial aquifers occur along the Rift Valley namely; Karonga Lakeshore, Salima, Nkhotakota, Lakeshore, Upper Shire Valley and the Lower Shire Valley. The greater part of Malawi is however underlain by crystalline metamorphic and igneous rocks of Pre-Cambrian to Lower Palaeozoic age, referred to as the Malawi Basement complex (Chilton and Smith-Carington, 1984). The bedrock is deeply weathered and it is this saprolitic material (commonly 15–30 m thick) which forms the principal aquifer over most plateau areas (UNDP/SADC, 1997).

Shallow wells are by far cheaper to construct than boreholes and are thus found in poor/remote communities. Throughout Malawi countless shallow wells are neither lined nor covered and are located close to the surface, near to waste dumps or pit latrines, making the water susceptible to high levels of contamination. It is the quality of drinking water from highly contaminated sources that needs to be addressed at the outset, to meet the Millennium Development Goals (MDGs) and other policies/targets. In particular, the authors of this paper are working on a simplistic ‘well-add-on’ system that uses plant extracts to remove microbiological contamination from the shallow well waters.

The bulk of published data on drinking water quality monitoring in Malawi has focussed on surface water, boreholes and chemical contamination (e.g. Chilton and Smith-Carington, 1984, Lewis and Chilton, 1984, Palamuleni, 2001, Maliro, 2002, Ndolo et al., 2002, Msonda et al., 2007 and Sajidu et al., 2007). Hardly any work has been undertaken on monitoring the water quality from shallow wells to assess seasonal changes over a period of time. Shallow wells are one of the most important types of water supplies for rural areas in Malawi – mainly due to their low cost and easy of construction. About 27% of the population in Malawi rely on water from shallow wells (Staines, 2002). This research work was undertaken to develop water quality data from shallow wells in three districts of southern Malawi namely: Balaka, Chikwawa and Zomba in 2006/07 (Fig. 2a). Seasonal changes in the biological, physical and chemical water quality parameters over a year are investigated. The study aims to establish if shallow wells can provide safe drinking water throughout a year or whether there is a need to develop ways to improve the water quality yielded from shallow wells. This study extends the data on shallow wells already documented for Blantyre, Chiradzulu and Mulanje between 2005 and 2006 by Pritchard et al. (2007).