Water-bath canning uses boiling water to process jars of appropriately acidic foods, such as many fruits, jams and tested pickles. Its suitability depends on the exact recipe and acidity, not simply whether a food tastes sour.
It cannot replace pressure canning for low-acid foods. Follow a tested recipe, including added acid where specified, jar size, processing time and altitude adjustment. A jar that seals has formed a vacuum; the seal alone does not prove safe processing.
Reference: Further reading.