Similar to egg white in appearance and consistency, aquafaba is simply the viscous liquid which is left over from cooking dried chickpeas and other legumes, and is used to replace eggs in a variety of baked goods, and savoury dishes.
Place the dried chickpeas into a large pan, and add the water.
Bring to the boil, cover the pan, then lower the heat.
Simmer for a couple of hours, until soft, keeping an eye on the pan to make sure it doesn't boil dry. If necessary, add a little more water.
Turn off the heat, and allow the chickpeas and aquafaba to cool in the pan.
At this point, you can decant the AF into a suitable container, and store in the 'fridge, plus do the same for the chickpeas (or use them in a meal or hummus, or even brownies). You can also freeze the AF in individual portions. Or do what I do, and store the whole lot in an airtight container, and remove the AF as and when needed. Doing it this way, I find, gives me a much nicer and thicker AF.
If stored properly in an airtight container, both chickpeas and aquafaba will keep in the 'fridge for up to a month. Frozen aquafaba should be good for around three months.
To use; simply sub 3 tablespoons of aquafaba for each egg or egg white.