Water Treatment and Dialysate Preparation
The treatment train
Municipal water → backflow prevention → particulate filters → water softener (exchanges calcium and magnesium for sodium, removing hardness) → carbon tanks (adsorb chlorine and chloramine) → reverse osmosis (removes ions, bacteria, endotoxin) → storage and loop → ultrafilters or UV at point of use. RO performance is tracked by conductivity and percent rejection.
Why each step matters
- Chlorine and chloramine are not removed by RO and must be carbon-adsorbed. Chloramine causes haemolysis and methaemoglobinaemia. Total chlorine is tested before each shift and after carbon changes - the most commonly tested water fact.
- Hardness: calcium and magnesium scale the RO membrane; softener failure shows as hardness breakthrough.
- Bacteria and endotoxin: biofilm in the loop causes pyrogenic reactions with fever and chills. AAMI/ANSI standards set limits for heterotrophic plate counts and endotoxin in water and dialysate.
- Chemical disinfection of machines and the loop requires residual testing before patient use.
Dialysate
Concentrate is proportioned with treated water. Typical final values: sodium 135–145, potassium 1–4, calcium 2.5–3.5 mEq/L, bicarbonate 32–39, plus magnesium, chloride, and glucose. Proportioning errors are dangerous: wrong concentrate or a failed proportioning pump can cause hyper- or hyponatraemia, haemolysis, or hypocalcaemia.
Rule of thumb: on a conductivity alarm, suspect empty concentrate or a proportioning fault - stop UF, clamp off the patient's blood lines, and correct before resuming. If haemolysis is suspected, do not return the blood.