I am using sigma waterstones for 2 years or longer. They are left in water for few days, than dried and stored for long periods. I worked a lot recently, and my stones were in water for 4 weeks. They were not exposed to cold, and from time to time water level lowered and they were not completely submerged. From what Stu posted, Sigma stones can be held in water indefinitely.
Just noticed that pink 6000 developed a crack, covering almost whole 2 sides. Nothing broke off, but crack is clearly visible. It is definitely not manufacturing issue, as I would notice it much earlier.
Is something wrong in keeping Sigma stones in water for long times? I don't see anything on other stones (120, 400.1000.13000) Should I do something to prevent replacement stone from having same issue? I know that there is no cure for the stone, once they fully separate. Only good thing is that crack is parallel with surface, almost on half of stone, and I hope I will be able to make base, and have 2 stones
Anyway, they perform so well that I won't hesitate to buy same type, even if lifespan is 2 years.