“…The hydraulic characteristics of the material have shown of the district softening plant upflow units, This unit showed a 15 per cent higher exchange capacity and a slightly lower salt consumption than the test unit with the same resin, due primarily to the greater efficiency of upflow operation, A recent economic study, comparing the polystyrene resin in the plant unit with the average of the zeolites used in softening plant operation, provided the data shown in Fig. 6, The following items were given consideration: [I] cost of exchange material; [2] cost of salt for regeneration; [3] cost of sodium silicate addition where required; and [4] value of the regeneration water lost. The unit charges for these items are listed in Table 5.…”