Potatoes and Onions Indian Style

I got this recipe from Tony Bilson's "Fine Family Cooking". I'm not particularly happy with it. I was expecting some deliciously sticky sweet and spicy potatoes, but it was more like a spicy chunky watery potato soup. The taste wasn't unpleasant, although it looked unappealing and did not go down well with the kids, my husband would eat it again but only served as a side (he'd prefer it beside a large steak). Tony says "This spicy mixture of vegetables is best served with Indian bread, such as chapatti, made from wholemeal (wholewheat) flour." It serves 6 as a main and i think you could get 8 to 10 out of it as a side. I followed these directions to the letter, please let me know if you can work out what i did wrong?

I
1/2 cup vegetable oil
4 teaspoons black mustard seeds
2 tablespoons finely chopped fresh ginger
1 fresh green chili pepper, seeded and finely chopped
1 tablespoon ground coriander powder
1 teaspoon turmeric
1/2 teaspoon ground paprika
4 cups potatoes, boiled and cut into small cubes
3 cups chopped onions
4 cups water
1 tablespoon salt
2 teaspoons lemon juice
3 tablespoons chopped fresh coriander leaves

M
Heat the oil in a deep pan or wok over a high heat. When oil is very hot, add the mustard seeds and cover the pan as seeds begin to pop. When the seeds stop popping and turn gray, after a minute or two, reduce heat slightly and add ginger and chili. Cook for 2-3 minuets. Add the coriander powder, turmeric and paprika. Stir add the vegetables and saute for 10mins, stirring frequently. Add the water and sprinkle the mixture with salt. Cover and simmer for a further 15 minuets. Stir in the lemon juice and sprinkle with the coriander leaves.