of  water  that  can  be  poured  into  the  well  is  an index of the well capacity when pumping; when saturated,  the  sand  yields  its  contents  as  freely  as it absorbs water. Often the raising or lowering of the  pipe  a  foot  or  more  brings  a  greater  length of the screen into contact with the water-bearing stratum and results in a great increase in yield. There are two methods of drilling wells, one is the hydraulic rotary and the other is the cable- tool percussion. Drilled wells tend to be the most complicated  and  require  a  lot  of  equipment.  In most  cases  Equipment  Operators  will  be  called upon to place drilled wells. The Utilitiesman may be  called  upon  to  install  pumps  and  plumbing when  the  drilling  is  complete.  Development  of  this type  of  well  will  then  proceed  in  a  similar manner  as  any  other  type  of  well. ALTERNATIVE  WATER  SOURCES In  some  regions  of  the  world  there  is  not enough surface or ground water available to sup- port  the  demands  for  domestic  and  fire  protec- tion  water  needs.  In  these  areas  it  may  be necessary to develop alternate sources of water. Rainwater,  snow,  seawater,  water  barges,  and mobile  tanks  are  a  few  of  the  alternate  water sources  that  may  be  considered. In  tropical  regions  there  is  an  abundance  of rainwater with a rapid rate of surface runoff. The construction of collection surfaces can be a solu- tion  to  water  needs. For temporary or emergency water supplies, collecting surfaces may be constructed by the use of  tarps,  wooden  platforms,  metal  surfaces,  and so on. Usually, however, surfaces constructed for other  purposes,  such  as  building  roofs,  may  be used. More  permanent  rainwater  catchment  areas will be cleared, graded, and given an application of  cement  or  other  impervious  mixture.  The catchment  area  should  be  located  at  least  100  feet from   any   source   of   subsurface   contamination (septic  tanks,  cesspools,  and  so  on),  and  as  far from  other  sources  of  pollution  (dust,  soot,  and so  on)  as  possible.  The  catchment  area  and impounding basin should be enclosed by a fence. Collected waters should be carried by gravity or pumping to closed stowage reservoirs. As rain falls toward the earth, it absorbs dust and such gases  as  carbon  dioxide  and  oxygen,  and, therefore,  must  be  considered  unsafe  for  con- sumption  until  treated.  Filtration  and  disinfection are  the  minimum  required  treatment. In  some  locations  water  may  be  so  hard  to obtain or polluted that it would not be economical to develop any source. In this case, water barges or  mobile  tanks  may  be  used.  Barges  or  mobile tanks  can  be  filled  from  ships,  tank  trucks,  or other well points located some distance away. It is  important  to  note  that  all  mobile  containers  are a  temporary  water  source.  Disinfection  of  their surfaces  that  will  come  in  contact  with  potable water is required. In  northern  arctic  areas  where  deep  wells cannot  be  sunk  through  the  thick  layers  of permafrost,  and  the  surface  sources  are  frozen solid,  water  must  be  obtained  by  melting  snow or ice. Ice is preferred to snow because it will yield more water for a given volume. Snow or ice may be  contaminated.  Therefore,  all  melt  produced should be treated before drinking. Approximately 5  cubic  feet  of  snow  is  required  to  yield  1  cubic foot of water. In emergencies, personnel can eat small  quantities  of  snow.  This  snow  should  be placed  in  the  mouth,  rather  than  being  sucked, to  prevent  chapped  or  cut  lips.  Only  small quantities  of  snow  should  be  consumed  in  this manner because consumption of large quantities will  reduce  the  body  temperature. Seawater  is  vastly  different  in  its  characteristics (as  well  as  in  the  methods  of  purification  used) from   other   surface   sources.   The   chemical characteristics of seawater are such that normal coagulation and filtration are ineffective as treat- ment  processes. In  developing  seawater  sources,  consideration must  be  given  to  such  factors  as  surf  action, saltwater corrosion, suspended sand and silt in the water,  living  organisms,  surface  oil  along  beaches, and the rise and fall of the water level with the tides.  If  the  equipment  is  located  on  sheltered bays,  harbors,  lagoons,  or  estuaries,  it  can  be supplied  by  intakes  built  in  the  same  way  as freshwater surface intakes. On small islands where there is insufficient surface and ground water, and on or near open beaches, intakes for equipment can  be  built  as  follows: 1. Saltwater   wells.  Beach  wells  should,  if possible,  be  used  in  preference  to  offshore  intakes. Wells  can  be  dug  to  tap  fresh  or  salty  ground water.  This  eliminates  the  problems  caused  by tides,  surf,  and  shallow  water  close  to  shore.  Such wells have an added advantage in that they can be  built  back  of  the  shoreline  under  natural overhead  concealment.  Driven  and  jetted  wells may  also  be  used  effectively  at  beach  locations. 9-13