Soak the white beans in a bowl with plenty of cold water and set aside.
Heat oil in a large pot, add onion and cook until softened for 5 minutes. Add celery and capsicum, cook, stirring until the vegetables begin to soften for 5 minutes. Add the garlic and cook for 1 more minute.
Season well with salt and pepper.
Drain the white beans that have been soaking, rinse with cold water, and add to the pot. Add the stock, water, potatoes and stir.
Bring to a boil, then reduce heat and simmer, uncovered for 50-60 minutes until the white beans are tender and cooked through.
Divide among bowls, garnish with parsley and serve.