It seemed to be an acute problem, possibly confined to a single batch of the water although with no traceability, record keeping, or lot/batch numbers that sort of detail is impossible to tell. According to one of the articles there was even an event where they went around swapping out 5 gallon bottles they had delivered to customers without providing a reason, but they weren’t able to recover all of that batch and didn’t notify anyone. That, plus other evidence suggests that they knew at least one batch of their product was potentially contaminated, and tried to cover it up, and didn’t notify customers that they had delivered known poison.
It could be anything. Too much or contaminated potassium bicarbonate or lye, byproducts of improper electrolysis (assuming they actually did electrolysis and that wasn’t just BS), cleaning products (bleach?) that were not adequately rinsed. The medical report said that the victims didn’t have an identified infection that could cause the liver failure but maybe it could be a result of bacterial or fungal cultures growing in the equipment producing something poisonous that went into the water?