Preheat the oven to 180C/350F/gas mark 4
Use a 20cm/8 inch square cake tin.
Grease and line the cake tin with greased greaseproof paper. Measure the water, dates and bicarb. into a bowl and leave to stand for about 5 minutes. Put the sugar and margarine into a bowl and cream together, then beat in the soya milk and the date mixture. Fold in the flour together with the walnuts and mix lightly until thoroughly blended. Turn the mixture into the tin and level out evenly.
Bake in the oven for about an hour until risen and slightly shrinking away from the sides of the tin. A warm knife should come out clean when inserted into the centre of the cake. Leave to cool in the tin for five minutes, then turn out. Peel off paper and finish cooling on a wire rack.