Heat a large frying pan until hot, then add the oil. Remove the sausages from their casings and crumble the sausagemeat into the pan. Cook for a couple of minutes, breaking up the meat with the back of a spoon. When it begins to colour, add the onion and cook for a further 5 minutes. Stir in the mushrooms and cook until they begin to soften.
Stir in the tomato purée, tomatoes, basil and measurement water. Bring to the boil, then reduce the heat and simmer for 10 minutes or until cooked through. Season well.
Meanwhile, cook the pasta in a large saucepan of salted boiling water according to the pack instructions until al dente, then drain. Spoon into serving bowls and top with the sausage sauce. Serve scattered with the Parmesan.