Water Treatment and Dialysate Preparation
The treatment train
Municipal water passes through a sediment filter, a water softener (which exchanges calcium and magnesium for sodium and protects the RO membrane from scale), carbon tanks (which remove chlorine, chloramine, and organic material), reverse osmosis (which removes most dissolved ions, bacteria, and endotoxin), and usually an ultraviolet lamp or ultrafilter before reaching the proportioning system. Two carbon tanks in series provide backup; test total chlorine after each tank, at minimum before each shift and after any carbon change.
Dialysate
Dialysate is made by proportioning concentrate with treated water-typically an acid concentrate containing sodium, potassium, calcium, magnesium, chloride, and dextrose, plus a bicarbonate concentrate. Conductivity reflects total ionic concentration and must fall within the prescribed range before the patient is connected. Bicarbonate concentrate supports bacterial growth and can lose potency, so it is used within the manufacturer's time limit.
Traps and a rule of thumb
Questions confuse the roles of the softener and the carbon tanks, or ask what happens if chloramine breaks through-hemolysis, worsening anemia, methemoglobinemia, and sometimes a chlorine taste. Another trap: the technician may test and record water quality but cannot redesign, repair, or override the treatment system-report out-of-range results and stop using the water per policy.
Rule of thumb: total chlorine after each carbon tank should be essentially undetectable (commonly less than 0.1 mg/L); if it is not, hold treatments and notify the person responsible for the water system.