If it is Plastic that is coming out then it will not be calcium deposits!!!!!!!!!!!.
Plastic is more likely to be the result of a dip tube breaking away as you have already been told by Harold.
If it is calcium deposits it is the result of hard water being heated when the calcium sparates from the water and deposits itself to the water pipe interiors etc.
The only way to prevent calcium from doing this is to install a water softener.
Hope this helps
Selgas Services Ltd
Craftsman Gasfitters, Plumbers, Electrical Service Technicians