Generally, whenever we clean water, we use RO for this, but you will be surprised to know that water can be filtered in a natural way also. Nature itself has made such arrangements that contaminated water can be cleaned.
Arsenic is found especially in the groundwater of the Ganga plains. Generally, water in such areas is treated and made drinkable.
Recently, new research has discovered a plant that absorbs arsenic from water. This is a completely natural and cheap process to remove arsenic from water. The School of Environmental Studies of Jadavpur University has done the research. Research has shown that the aquatic plant Pistia Stratiotis has the ability to absorb arsenic from water.