Water is an essential compound for all forms of life in the
Earth planet. Springs and groundwater are the two main
sources of water used for domestic and other social purposes
in Zanzibar. The exploitation of water from groundwater
aquifers has become a common practice in different areas of
Zanzibar Island. Moreover, during rainy seasons, rainwater is
also a potential source of fresh water for domestic and other
social purposes and activities.
The issue of water quality is very poignant in many
countries, but the vulnerability of water to contaminants due
to natural and anthropogenic sources has become a common
problem worldwide 1.Water is an inevitable need to man
and his environment; it has existed throughout the history of
the earth crust even before the existence of man. However,
the water qualityis persistently pollutedin many countries of
the world 2.
The importance of water quality for the health of human
being and welfare is of a great interest and attention in the
world. Access to sufficient, clean, and safe water is essential
for human survival, and is one among the fundamental
human rights. Regarding public health, limited access to safe
water obviously undermines other public sectors such as
public health, which can lead to communicable diseases. The
46 Abdul Ali Juma Mohamed et al.: Risk Assessment on Trace Metals in Groundwater and
Springs in Urban Environment of Zanzibar Island
provision of potable drinking water has been highly
assembled in national and international documents 3.
The issue of water quality is one of the poignant agenda in
many countries. The exploitation and utilization of water
from groundwater aquifers has become a common practice in
different areas of Zanzibar Island. Nevertheless, the
vulnerability of water to contaminants due to natural and
anthropogenic sources seems to be a common phenomenon
1. Moreover, both the qualitative and quantitative aspects of
water resources might be vulnerable to deterioration due to
environmental degradation. Very recently, about 2.7 million
liters of water are anticipitated to be lost at Chunga water
supplies located at west region of Zanzibar owing poor
utilization of the environment.
Fresh water supply is an important concern worldwide,
about 90% of fresh water in the world originated from
groundwater aquifers 4. An aquifer is an underground
component of saturated earth materials that can provide
usable quantities of ground water to a well 5.
In Zanzibar, rapid rate of urbanization has increased
demand of water, which necessitated the usage of
groundwater to supplement the existing water supply
systems, in most areas of the Island. Accordingly, the trend of
developing privately owned water wells has increased to an
amount that has outnumbered the public and community
water source 1.
Water resources evaluation typifies a major concern of the
present world due to the importance of water for human
being and society in general 6. Good water quality
management is fundamental for the production of clean water
for the human consumption and safety. Qualitative as well as
quantitative determination of the contaminants, along with
the predictions of their possible source(s) are vital in an
attempt of tackling contamination problems in groundwater
and surface water 1. Therefore, an evaluation of drinking
water quality is a crucial concern for implementing
sustainable water-use strategies, plan, and policy.
Moreover, information about water quality analysis is
always used as a basis to discuss utilizing groundwater in
order to avoid associated water illnesses and health
problems. 7 Groundwater quality depends, to some extents,
on its chemical composition. Monitory of the levels of
cations and anions play important and indicative role in
assessing degree of groundwater contamination 8.
Nevertheless, an access to good water quality supply and
sanitation services has become a hot issue in most of
developing countries, and still these services do not reach a
significant proportion of the world’s population. It has
become a more challenging agenda due to factors such as
rapid rate of urbanization and environmental pollution.
Harmful impurities from various sources such as,
agricultural and domestic effluents, municipal sewerage are
among the key factors, which deteriorate the quality portable
water 9. Trace metals are among a wide range of
contaminants, which receive health concernsdue to their
potential toxicities even at very low concentrations. Trace
metals gain entrance into human systems via contaminated
drinking water, air, and food. In the body, the metals can
compete with, and displace essential minerals such as zinc,
copper, magnesium, and calcium; and interfere with body
biological organs, systems and functions 10 Over a certain
period, metals have tendency to bio-accumulate in tissues of
living organisms 11. However, some trace metals (such as
zinc, copper, iron, and manganese) are the micronutrients;
the body in small amounts for metabolic activities requires
them. At higher concentrations, these same elements, can
cause adverse health effects or illness 12.
Toxic metals such as cadmium (Cd), lead (Pb), arsenic
(As), chromium (Cr), and thallium (Tl) do not have
beneficial effects in humans. Long-term exposures to these  

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