Holly:
You can help keep it from turning bad really quickly by just adding more water and a good dose of salt. I've found that the dose of salt for such purposes must be pretty large (a few good pinches); if there's too little, the salt from the cheese is drawn out in to the water and you have unsalted mozzarella, which is pretty dull. On the other hand, I've never added so much that I thought the cheese had ended up appreciably saltier than it was supposed to be. This technique I use as well with feta and haloumi.
But remember, for mozzarella freshness is of the greatest importance. Don't wait: eat it now and buy some more when the tomatoes are ready. It will in any event only stay edible for a matter of days, unless they have performed satanic rituals over it.
In general, I would suggest checking the dates of lots of containers, find the most recent one, buy it and take it home; eat it that day fresh. If there's any left over, use it for cooking, where it can also be quite delightful.
Antonius
Alle Nerven exzitiert von dem gewürzten Wein -- Anwandlung von Todesahndungen -- Doppeltgänger --
- aus dem Tagebuch E.T.A. Hoffmanns, 6. Januar 1804.
________
Na sir is na seachain an cath.