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Condis crystals my Gran used, I wouldn't suggest though, rough salt over night may do.

Not sure about snails in your region, if in doubt wash thoroughly with salt and cook in butter, perhaps not the fresh you looking for but most definitely safe.

I've never had it cooked! I would like to try that.

Found some tips for you to try from a local forager watercress have fun with your fresh supply.

Great watercress tips! There is much there that I didn't know. Thanks for thinking of me.