water filled the dry chemical 22 will therefore dissolve in the water in inner chamber 27 producing a charge of water containing a concentration of the chemical when the pump is operating the water chemical solution is forced out of inner chamber 27 as indicated by arrow f into pipe 23 and via metering valve 24 and pipe 25 into well casing 13 as the water and chlorine solution flows into well casing 13 it will temporarily raise the static level of water 26 when pump 14 ceases to operate the weight of the water chlorine mixture and the normal atmospheric pressure will cause the static water level 26 to return to its normal level thereby pushing untreated water downward as will now be recognized this action advantageously permits the well casing 13 and standpipe 12 to serve as a retention vessel metering valve 24 is adjusted to cause the flow of water from outlet 17 to be in the range of 2 10 of the pump output assuming that the system has just been put in operation this action will be repeated on each cycling of pump 14 and at some point in time the water and chemical solution will reach the inlet portion of pump 14 and will be drawn into the pump as indicated by arrows a the concentration of chemical 22 in the water flowing from pipe 25 will depend upon adjustment of metering valve 24 and the periods of operation of pump 14 advantageously chemically treated water will be added via pipe 25 only when pump 14 is running during the period of retention in well casing 13 oxidation or chelation will be proceeding by testing the residual chemical in water flow c the correct setting.