Preheat oven to 180 C / Gas 4.
Lightly grease a 13x23cm loaf tin or a 20cm round cake tin.
Sieve together the flour, sugar, cocoa, bicarbonate of soda and salt.
Add the oil, vanilla, vinegar and water.
Mix together until smooth.
Pour into prepared tin and bake for 45 minutes.
Remove from oven and allow to cool.