Prepare a water bath canner for hot pack (water simmering at about 180 F) before beginning, and also prepare jars, lids, and rings.
Prepare the quince by peeling, coring and slicing. Be careful here, quince are very hard to cut, watch your fingers.
Add the water and sugar to a large pot and bring it to a boil, stirring to dissolve the sugar.
Add the sliced quince, return to a boil and then turn the heat down to low.
Simmer the quince covered until they're fork tender, pink and fragrant (about 30 to 40 minutes, or longer, depending on the variety). Add water as necessary to maintain the liquid level.
Remove the quince from the heat and use a slotted spoon to pack into prepared canning jars, leaving 1/2 inch headspace.
Ladle the cooking liquid over the quince in jars, maintaining 1/2 inch headspace.
Debubble jars, adjust headspace, apply 2-part canning lids and seal to finger tight.
Process jars in a water bath canner for 20 minutes (pints) and 25 minutes (quarts), adjusting for altitude (see below).
When the canning time is complete, remove the jars to cool on a towel on the counter. Check seals after 12-24 hours, and store any unsealed jars in the refrigerator for immediate use.
Properly canned and sealed jars of quince will maintain peak quality on the pantry shelf for 12 to 18 months, and be good to eat for much longer. Refrigerate after opening.