I am a person having installed a biogas plant in my house and is being used. Rice water is of course good for producing gas. But if one is going for a biogas plant it should be usable to manage the waste of the house. Waste does not include plastic or paper wastes. Only bio-degradable waste should be used.
If you use a plant with a capacity of four to five kilogram waste, you will get gas for burning about two hours. But remember that this gas has no pressure equivalent to that of LPG, hence more time will be required for boiling rice or water.
Very often two hours will not be sufficient for a family to do all their cooking needs. Hence biogas plants can help reducing the use of LPG. These days all the families are short sized. (Remember that a biogas plant mentioned above will cost around Rs.12,000/- or more. Subsidies to the tune of 50% or more are available, if fitted through the Panchayath.
Gold Member, SPK