How do you make fuel out of water?  ?

You can use electrolysis to split water into hydrogen and oxygen:

2 H2O --> 2 H2 + O2

When those two are reacted to form water, energy is released. 

use electrolysis to convert H2O to H2 + O2
reduce CO2 from atmosphere to COuse fisher tropsch method to convert CO + H2 to hydrocarbons  CxHyreact CxHy (fuel) + O2 to form CO2 + H2O

Add energy and split the water back into H2 + O2.  Then burning the H2 + O2 will produce energy.  But please realize there are inefficiencies in any real world process and you will not get as much energy out as you put in.  In other words, trying to turn water into fuel is a losing proposition. 

Water is an oxide, which means it is a product of combustion. In other words, it is an ash, of sorts. If you desire to make water into a fuel, then you need to reverse the combustion process by adding energy. Splitting the water molecule into Hydrogen and Oxygen will accomplish this, and the Hydrogen then is your fuel. 
Cheers. 

step 1
poop in water
step 2
profit

You bottle it and make lots of profit selling the water so you can buy fuel. You can convert water to hydrogen, but that costs more money than the energy you get back.

You are right derfram, you won’t get as much energy back, the same can be said about electric cars. I suppose if the energy source is green and renewable, it’s a feasible solution.