There are several websites with tips and ideas on how to save water. Earth Easy offers 25 things one can do at home to conserve water. Water Wise and Save Water also have tips on how to cut back on one's water usage.
you 4000 galloons of fresh water that you could be saving water
They could be saving up to 15,000 to 25,000 gallons of water a year.
By saving water, we can save life of many creatures of the world who directly or indirectly depends on water.
Depends on what you do with the water you save or the money saved. Could help, but if you just save it and keep it in North America, no.
It probably could.
Refer to the State Geological Survey for information regarding groundwater supply, and possible location.
By saving water, we can save life of many creatures of the world who directly or indirectly depends on water.
Information on the Viscosity (how easy it flows) of water can be found on the Wikipedia page for Water. Here it has information on the Viscosity of water in its various states (Solid, Liquid and Gas).
conservation of water means saving water
No drinking water is necessary for your life
With out a better description of what the power saving device is and how it is connected into the water heater's circuit, an answer can not be forthcoming. If the device is connected in series with the "hot" line of the heater and it opens the lines up then of course the hot water tank will not work. If you go to the discussion page and leave more information, an answer might possibly be found to your question.
saving the water