Spokesman Kerry Williamson says one patient who was sent home from an Edmonton hospital has been readmitted as a precaution due to the death.
The other two continue to receive care at Royal Alexandra Hospital.
AHS has said a worker opened a wrong valve during regular system cleaning last week, and a chemical was released into the water used for dialysis of the four patients.
The chemical was a combination of peracetic acid and hydrogen peroxide, which would cause reaction like a sunburn inside the body.
Health services president Vickie Kaminski has said the exposure was limited to a few minutes and it's not yet known if the patient's death was connected.
She said the agency is conducting a review to ensure the error doesn't happen again.
Workers are installing extra lockouts on valves, improving valve indicators and posting better signs to ensure the water supply is protected from contamination.