There are several issues he

1) legums (beans, peas, lentils) are soaked in water over night to
reduce cooking time and to leach out certain toxic compounds
(haemagglutinins). In some species the haemagglutinins are heat labile,
and the soaking water can be used for cooking as well. In other species
haemeagglutinins are heat stable, and the soaking water needs to be
discarded and replaced with fresh water for cooking. I find it too much
trouble to remember which legums belong into which category, so I
routinely discard the soaking water, so I am always on the safe side. A
good cooking book however should contain this info, if you are
interested.

2) The soaking water will contain a small amount of minerals, and may
be some water soluble vitamins. Amounts will be limited however, and if
you add some root vegetables (carrots, tunips, celeriac, potatoes and so
on) after the legums are almost done, that should take care of it. Note
that not only acids, but also salt should be avoided until legums are
soft.

3) Flatulence from legums can be reduced by certain spices, most notably
caraway seeds and the leafes of Satureja hortensis (Labiatae), (does
anybody know the Englisch name?) In German it is called *Bohnenkraut*
(bean spice), as it goes particularly well with beans. In the garden
even a small patch of that herb will emanate an intensive, pleasant
fragrance, and attract a lot of butterflies, bumble bees and the like.

4) If need be, flatulence may be treated by drinking a tea from equal
parts of caraway, anis and fennel seeds (2-3 cups per day, between
meals, using a good tea spoon of seed mixture per cup of boiling water
and soaking for 10 min).

5) Potatoe boiling water does contain some minerals and vitamins, and
also a lot of flavour, if potatoes are boild after peeling. The potatoes
are then rather bland, with a slight salty taste from the salt added. A
better procedure is to peel them after boiling, the water-impermeable
skin protects most of the goodies from leaching into the water. There is
no point in adding salt to the boiling water in this case, as it would
not get into the potatoes either. But because the natural flavour of the
potatoes is protected, salt is not required, which is beneficial for
health.