How do they store enough oxygen to last until the next supply shuttle comes on the ISS??

Question: How do they store enough oxygen to last until the next supply shuttle comes on the ISS??
- Keywords:
  ISS,
  oxygen,
  shuttle,
  spacecraft
Asked by Anon to Rochelle, Julia, Jon F, Beth, Adrian on 18 Jan 2016.
- Jon Farrow answered on 18 Jan 2016:
  
  A lot of the ISS’s oxygen is stored with two Hydrogen molecules parked next to it – as water (H2O)! When they need oxygen, the system breaks the water molecules apart using electricity, vents the Hydrogen overboard, and gives the crew oxygen. The carbon dioxide they breathe out is scrubbed out by fancy air filters and vented overboard. They are really good at recycling water, but they still need to keep bringing up water with every supply ship (that comes every few months).

Question: How do they store enough oxygen to last until the next supply shuttle comes on the ISS??