By absorbing water, minerals and air through free surface of entire plant body.
They can grow in soil and water with sunlight. plus all plants can not live without water.
Water cycle
Magically make plants grow on it, and make water stay on it.
Plants need water to make glucose. Glucose is a sugary substance that plants make. Glucose is the food that plants need to live. So yes, plants do need water.
Most plants grow best if they are in an area where they can receive plenty of sunlight and water.
There are several types of plants that grow in ponds some are lillies, and some green type of plants that grow flat on top of the water. Here is a web site I found. http://www.watergarden.org/Shade-Plants
nasa has successfully used hydroponics to grow potatoes in space. all you need is a temperature which is suitable for your plants to live and water.
Water helps plants grow
You should take care of plants so that they grow and continue to live. If you do not water plants and give them sunlight they will die.
The reason that the majority of aquatic plants grow near the surface of water is sunlight- the deeper you go, the less light makes it through the water. Because plants need sunlight for photosynthesis, most will then grow in shallower water because they will have more light.
Freshwater plants grow in ponds, lakes, rivers, and streams. Most have roots which anchor them in the mud at the bottom. Their stems grow through the water and their leaves and flowers open above the water's surface.
Water helps us to live because it keeps us hydrated. It also is important to plants to help them grow which are fed by animals and people eat both animals and plants to live.