Question
After a year in water and leave that have turned yellow, can proper care turn the leaves green again?

Answer
Hi Hanna,

The Latin name for genus of the "mother-in-law" or "snake" plant is _Sempervivium_, which interpreted literally means "always alive".  That very succinctly describes the tolerance of these plants to environmental extremes.  So, the possibility of your plant recovering is very, very good provided you follow some general culture protocols.

These particular plants come from tropical regions which experience very wet and very dry conditions during the annual cycle.  Resultantly, there are times when the roots are completely saturated with water, and other times when they are almost completely dry.  These plants are succulents, meaning that they can store and use water very efficiently.

If these have been in water for a very long time, move them out of the water into a porous, damp potting medium such as milled peat moss (or any commercial potting medium).  Until the plant's roots penetrate into the medium and provide support, you may need to support the plant with a stick, etc.

If the leaves have turned completely yellow, that may indicate a problem with the root system or, more likely, a lack of nutrients, specifically iron and magnesium.

After you have moved the plant into a pot, do not provide any nutrient supplements for approximately a month as the new potting medium will have enough nutrients to last that long.  If the plant has NOT been in a sunny location, place it in a well lit (no direct sunlight) area.  Slowly, you can give the plant more and more sunlight until it is in direct sunlight.  If you can, move the plant outdoors when the weather permits and gradually place it into a sunny, well-lit location.  

Your plant should thrive.  (Mine has even bloomed outdoors.)
Good Luck and Good Gardening.