CHAPTER ONE
INTRODUCTION
1.1    Background to the study
Water is a vital resource for every human activity. Water makes life possible. Without it, life and civilization cannot develop or survive (Ojekunle, 2011). Water forms the largest part of most living matter and is vital  to  man  just  as  air  and  food  are  (Ayoade,  2003).  The management and maintenance of water is thus very important (Fiorilloa, 2007). The  accelerating  growth  of  human  population,  the  rapid  advances  made  in  industry  and agriculture  have  resulted  in  a  rapidly  increasing  use  of  water  by  man,  to  the  extent  that  the availability of water as well as the control of excessive water has become a critical factor in the development  of  every  regions  of  the  world  (Williams,  2010).  
Over  the  decades,  water  supply management  has  proved  to  be  insufficient  to  deal  with  strong  competition  for  water  with growing  per  capita  water  use,  increasing  population,  urbanization  pollution  and  storages (Wang  Xiao  –  Jun  et  al, 2009).  In addition, the need for domestic, industrial and agricultural water supply is growing, but the absence of demand management strategies means that the increase in demand will likely outstrip the available supply, hence water scarcity (UNESCO, 2006). One-third of the world’s total population of 5.7 billion lives under conditions of relative water scarcity and 450 million people are under severe water stress (UN, 1997). The issue of water scarcity in the world and its implication on development of new political and economic  relations  among  countries  may  result  to  crisis  in  the  future.  Thus, there is need for the implementation of effective water resources management which becomes particularly important towards determining how much  water  is  available  for  human  use  and  economic  activities  that  water  should  be shared between  users.
Population growth is a major contributor to water scarcity.  The global population is expanding by 80 million people annually, increasing the demand for freshwater by about 64 billion m3 a year (Population Institute, 2010). Rapid population growth and urbanization could expose more people to water shortages, with negative implications for livelihoods, health, and security. These demographic trends, coupled with increasing per-capita water consumption, will be a huge development challenge (Bates, Kundzewicz, Wu and Palutikof, 2008).  Growth    in population implies mounting demand and competition  of  water  for domestic, industrial, and municipal uses (Population Action International, 2011). Population  growth  leads  directly  to  increases  in  overall  water  demand,  while  other demographic factors such as population distribution and age structure modifies the pattern in demand and determines  increases  in  household  water  demand.  Overall, the amount of water each person uses is expected to increase as incomes grow and consumption increases (UN-Water and FAO. 2007).
Evidences are ample that there is an explosion in the population of cities in Nigeria (Eja, Inah, Yaro and Inyang, 2011; Nwosu, 2013). The effect of the rapid urban population growth is noticeable through the provision of municipal services such as pipe-borne water. Expectations of the populace on the activities of policy makers for the supply of water are quite high. (Sule, 2008). Water can be said to be adequate when an individual is availed a quantity of at least 50 litres per day (World Health Organization, 2003).  
The unavailability of water in required proportion for man’s use has assume global crises dimension. According  to  the  Population  Institute  (2010),  only  20  percent  of  the  global  population  has  access  to running water and over 1 billion people do  not have access to clean water. The Population Institute noted further that with a projected population of the world to expand to 9 billion people by 2050, it is estimated that 90 percent of the additional 3 billion people will be living in developing countriess, many of which are already experiencing water stress or scarcity therefore, it is pertinent to manage water resources sustainably.
Water resources management has a significant impact on the socio-economic development of a catchment. The water demands and availability depends on the economic, ecological, land use, and climatic changes of a region (Droogers,2012). Water resource management is a multifaceted issue that becomes  more  complex  when  considering  multiple  nations’  interdependence  upon  a single shared trans boundary river basin (Teasley and McKenney, 2011). The  management  of  water  resources  as  a  common  resource  would  require  trade-off  among  countries  and  water users (Yang and Zehnder, 2007). The need therefore to devise means by which available water can be consumed and allocated among the various uses is pertinent.
The planning of human activities involving rivers and their floodplains must consider hydrological facts; (…) the flows and storage volumes vary over space and time (Loucks et al, 2005).  The  necessity  of  predicting  the  hydrological  patterns  is  essential  to  the  reservoir management.  The  reservoirs  have  to  insure  not  only  the  water  quality,  but  also  the  human,  the industrial  and  the  agricultural  consumption. Nowadays the environmental concerns such as the aquatic biodiversity and the environmental pressure have an increased influence in the decision-making.
Asa River is one of the major sources of water supply in Kwara state. This study simulates the hydrological process of Asa watershed that allows for the estimation of available water resources, so that sustainable and rational utilization, conservation and management of available water resources will be adopted using Soil and Water Asessment Tool (SWAT) model. The study also proffers alternative strategies for water conservation that will meet water demand within the basin.