To  Make  a  Simple  Filter. — Build
in  an  8-inch  partition  wall,  after  the
bottom  has  been  paved,  to  a  point  a
few  inches  higher  than  the  outlet  of
the  overflow  pipe.  Lay  up  the  first
10  or  13  inches  at  the  bottom  of  this
partition  (4  or  5  courses  of  brick)
without  cement  for  the  water  to  pass
through.  Plaster  the  upper  jjortion
of  the  partition  with  cement.  Or
build  the  entire  partition  with  soft
porous  brick  laid  in  cement  but  with-
out cementing  the  outer  surfaces.
The  water  will  be  filtered  very  well
for  a  while  by  passing  through  the
brick,  but  in  time  they  will  become
foul  and  clogged.  It  will  then  be
necessary  to  tear  out  the  partition
and  rebuild  it.  Hence,  it  is  better,  if
the  first  cost  can  be  afforded,  to  pro-
vide a  separate  chamber  containing
proper  filtering  materials.
To  Build  a  Double  Cistern. — Con-
struct a  small  compartment  (A)  into
which  the  water  from  the  roof  is  to
be  received.  Build  next  to  this  the
filter  chamber  (B).  Fill  this  from
the  bottom  upwards,  4  feet  in  depth
in  all,  first  with  pebbles  the  size  of
the  fist,  then  with  very  coarse  gravel,
then  fine  gravel  and  lastly  sharp,
clean  sand.    Screen  these  materials  to


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proper  sizes  and  wash  them  clean  and
free  from  loam  and  other  impurities.
