MIT OpenCourseWare http ocw mit edu 11 479J 1 851J Water and Sanitation Infrastructure in Developing Countries Spring 2007 For information about citing these materials or our Terms of Use visit http ocw mit edu terms Water Sources Improved and Unimproved and Water Supply Planning Susan Murcott Week 4 MIT 11 479 J 1 851J March 5 2007 Photo Donna Coveney Water on Earth the Hydrologic Cycle Condensation Advection Precipitation Condensation Sublimation Precipitation Ice and Snow Transpiration Melt Runoff Evaporation Runoff Evaporation Soil Moisture Lake Infiltration Ocean Groundwater Flow Groundwater Figure by MIT OpenCourseWare Water on Earth Seawater 96 5 Ice and Snow 1 76 Atmospheric Water Sub Total Freshwater Available Groundwater 0 001 98 26 1 74 1 7 Lakes 0 013 Rivers 0 002 Total 100 Shiklomanov I 1993 Fresh water lakes and rivers also known as surface waters Fresh water lakes and rivers which are the main sources of human water consumption contain just 0 01 of Earth s total water about 90 000 km3 of water Average Renewal Time for Various Water Resources Atmospheric Water 8 days River Water 16 days Soil Water 1 year Wetlands Water 5 years Lake Water 17 years Groundwater 1 400 years Clarke R 1993 Reliable Run off Surface waters supplied by run off are further limited because more than twothirds of all run off is due torrential rains floods or from precipitation on uninhabited land Thus the amount of reliable run off available globally is only 9 000 km3 year Surface Water Run off km3 year World Run off from Land Surface polar zones excluded Unreliable Run off due to torrential rains floods etc 2 3rds of World Run off Reliable on Uninhabited Land 40 000 5 000 Reliable Run off 9 000 26 000 Clarke R 1993 Sources of Drinking Water Major Sources Rainwater Surface Water Groundwater Minor Sources Seawater Saline water Dew Fog Rainwater Pristine Surface Waters Pristine Ground Water Surface Water Stream Kenya Surface Water Rivers Nepal Surface water is frequently contaminated by human and animal waste in many parts of the developing world Feces and Trash Groundwater Usually free from pathogens Filtered by soil Contamination due to poorly sited latrines or poor well construction Susceptible to contamination in karst areas May contain metals Fe Mn or hydrogen sulfide H2S Yields in some areas may be too low for practical use May be too deep to use economically May not be available everywhere Usually need pumps exception artesian flow Well construction can be difficult dangerous expensive Water is recharged to the ground water system by percolation of water from precipitation and then flows to the stream through the ground water system USGS 2006 Water pumped from the ground water system causes the water table to lower and alters the direction of ground water movement Some water that flowed to the stream no longer does so and some water may be drawn in from the stream into the ground water system thereby reducing the amount of streamflow USGS 2006 Contaminants introduced at the land surface may infiltrate to the water table and flow towards a point of discharge either the well or the stream Not shown but also important is the potential movement of contaminants from the stream into the ground water system or naturally occurring toxins such as arsenic or fluoride USGS 2006 Pollution of Wells Poorly Protected Well Groundwater is polluted Well too close to pit latrines soakaways refuse dumps Karst geology Drill hole To house Seepage from surface Slope ground away from well Grout well and install concrete apron Divert water away from well to soakaway 10 m away from well Properly Protected Well Steel casing To house Cement grout Uncontaminated water Contaminated water Figure by MIT OpenCourseWare Pollution of Wells Vessels for drawing water Contaminate water after contact with ground Design so buckets and ropes can t touch ground Permanently attach buckets and ropes to prevent removal Use collapsible buckets Pollution of Wells Rubbish thrown down well Keep children and irresponsible people away from well Guard or attendant may be necessary Surface water May wash or be splashed into well Ground surface around well may be sunken Build headwall around well or cover Divert surface runoff from well Spilt water Water splashes on people s feet and back into well Can spread Guinea worm Unimproved Water Supplies as defined by the WHO UNICEF Joint Monitoring Programme Unprotected well Unprotected spring Vended water includes bottled and bagged water Tanker Truck water All surface waters Unprotected Well Hand Dug Well Hand dug well Most common Low capital costs but labor intensive Dangerous to construct without proper skills 1 5 2 0 m diameter 1030 m deep Pump not a feature of an unprotected dug well Unprotected Well Nicaragua San Francisco Libre Nicaragua Unprotected Well Kenya Nyanza Province Kenya Unprotected Well Burma Zimbabwe Finishing handdug well Unprotected Spring Vended Bottled or Bagged Water Vended Tanker Truck Water Vended Water Surface Water Ghana Surface Water Stream Nepal Improved Water Supplies as defined by the WHO UNICEF Joint Monitoring Programme Public standpipe Borehole drilled well Protected dug well Protected spring Rainwater harvesting Household connection Outside the home Inside the home Public Standpipe Photo Monique Mikhail Public Standpipe Drilled Well Types Driven tube well Driven tube well Perforated tube with well point driven into ground with hammers pile drivers etc 5 10 cm diameter 15 20 m deep Pump required due to small diameter Generally last 5 years as well points clog or rust Well point Bored tube well Dug with auger hand or mechanical Soil must be cohesive or can use casing Pack area around well screen with gravel to improve recharge 10 25 cm diameter 20 40 m deep Pump required due to small diameter Figures by MIT OpenCourseWare Well Types Jetted Tube Well Jetted tube well Tube jetting into soft material Soil removed from hole as sediment laden water flows out top 10 25 cm diameter up to several hundred m deep Pump required due to small diameter Usually cased Borehole Bore hole wells Require mechanical drilling rig Rotary type drills most common 15 30 cm diameter can be drilled deep as required Pump required due to small diameter Usually cased unless in bedrock Figures by MIT OpenCourseWare Jetted Tubewell Nepal A Protected Well A well equipped with Handpump Concrete Platform Drainage Channel Still protected wells can have problems Broken apron Broken handpump Use of