Groundwater as source of contamination for water supply in rapidly growing megacities of Asia: Case of Karachi, Pakistan

Abstract

The development of essential services including water and sanitation in many megacities of the economically developing countries of Asia cannot keep pace with their rapidly growing population and accompanying urban and industrial development. The inadequate water supply and poor sanitation services lead to contamination of their water supply through the input of sewage water into groundwater. This paper examines the problem of contamination of water supply in Karachi, the largest city in Pakistan with a population of over 12 million and growing at 6 percent per annum. The paper presents the data on water quality from various sources, mainly municipal water supply, vendors and well water; the three major sources of water for domestic use in Karachi. Except municipal water from some areas and during certain periods, water from most other sources contains coliform bacteria, and in many cases faecal coliform, in amounts several magnitudes higher than any standards permit. Many samples have also been found to contain heavy metals including chromium, lead, nickel and arsenic in amounts excessive of permitted standards. The probable sources of contaminants for the various types of water (piped, vendors, wells) indicate that groundwater may be the main contributor. The very source of this groundwater is predominantly from sewage. The paper also evaluates the solutions that are being practised, proposed or may be feasible, as well as those that are evolving.