In a saucepan, bring water, tomatoes and onions to a boil. Simmer for 5 minutes.
Add green beans, green pepper and fish sauce to taste. Cover and simmer for 5 minutes again.
Pour in sinigang mix. Increase the heat and bring toa boil.
Add the pork. Simmer for 40 minutes in a low medium heat until the pork is tenderly cooked. Turn off the heat and add the leafy vegetables. Cover to cook.