Water alone cannot fully replace healthy soil as a growing medium, but there are methods to regrow certain vegetables just by using water.
Plants like lettuce, cabbage, celery, and leeks can regrow shoots by placing their base in contact with water. Place one of these vegetables in a glass or dish of water and place the container by the window so the vegetable is exposed to sunlight. New leaves will grow within a week or two.
For garlic, take a clove and suspend it on the rim of a glass so only the base touches the water. A simple toothpick can be used to suspend the clove. The same method can be used for an onion bulb.
Though these vegetables will not regrow completely, the new shoots may be used to garnish dishes. For vegetables to regrow, they would need new roots and must be planted back in soil. Water can help in this as some vegetables can regrow roots by just using water.
Herbs like cilantro, thyme, and basil only take one sprig to regrow the whole plant. When choosing a stem for regrowing, choose one that is a few inches long before its first leaf node. Submerge the base of the sprig in water and once roots have grown to more than an inch, transfer the sprig to the soil.
For tubers and gingers, a toothpick can be also used to suspend the crop in a container. Position the tuber with one eye facing upward. Once roots have grown, bury the sprouted tuber and harvest it a year later.
For ginger, make sure to keep its environment between 10-20 degree Celsius as it thrives in tropical conditions. Replant the ginger in soil once roots and a green shoot have grown.