Package of 50 tablets; each tablet purifies a litre of water against bacteria, protozoa, and viruses.  The tabs are a measured dose sodium dichloroisocyanurate, certified and approved for use by NATO, Unicef, Oxfam, and International Red Cross (to name a few). 

Aquatabs don't add any chemical flavour to your water and won't stain containers.  After adding the tab to your water, wait 30 minutes before it is safe to drink.