Welcome to HCM
We understand your concerns
I went through your problem description. I suggest you not to worry too much. Water alone cannot cause such a problem. You need to get convinced on that matter. Water is very much essential for our body and it can only harm you when it is contaminated. Have you thought in this angle? You also say that it happens sometimes. That means it is occasional.
Keep a record of such stiffness
and note down what you ate on that whole day, which water you used etc. Include all information of that day if possible. You should come to know the cause yourself. Or else you can consult a physician for better advice.
Hope this clears your doubts. Available for further clarifications.