I bought this set of 3 saucepans in a clearance sale at the end of April, for use with a new induction hob. I have only just had the hob installed and started using the pans, but after first use each one turned mottled and discoloured on the base inside. No amount of washing will remove the stains. The water in my area is extremely hard, and I'm wondering if this is the cause? John Lewis no longer sell this set but have offered to replace with an anodised set instead - but I like the stainless steel ones. Not sure what to do! Any advice, please? 