Hello again, I've had too much time on my hands this afternoon and the Devil found me some mischief.. I looked up Sandy King's article and quite a long way down I discovered: "In most localities it is safe to mix the working solutions with tap water." As it's been a rather rainy month, the quality of tap water may have changed unexpectedly. Sandy suggests distilled water if the mains supply causes problems , but not apparently for ordinary use. Another straw to clutch.