You need handful of whole almonds (about 200g-250g). Put them in bowl and add bottled or filtered water, cover with plate and leave in fridge overnight. At the morning pour mixture in high container and blend it firmly. Put mixture through a sieve to separate grounded almonds.
That’s your base, now you add some more water to make it less strong.
It depends on your taste. I usually add half of liter of water. Some people add honey or Stevia sweetener to it, to make it more tasty. I don’t to keep it low caloric and sugar free.
Keep it in glass container like bottle or jar.