Here's site talking about half-gas/water mixture that works.
http://www.betterworld.com/BWZ/9608/product.htm
Had a couple of friends who had an old junker with a gas tank leak. They added another small tank and left the original in place. Their biggest thrill was to go to a "gas" station and fill up the tank with water, get out a bag of moth balls and argue about how many to add then drive off after making sure people noticed them.
Commuting to NYC during the Carter gas rationing days was a hassle.
I was managing a company in NYC but had no company vehicle.
Company cars got tanked up full every day no problemos - the little guy commuting got the Carter shaft.
Using two cars I swapped the front plates and by going daily to two different gas stations to get the small allowed ration was step #1.
Step #2 was to use an el cheapo adjustable aquarium device that metered air flow.
I used large plastic Coke bottles filled with tap water and a tad of ahcohol to run thru clear plastic lines up to a carb vacuum source.
It does not sound like much but my mileage increased enough for me to weather the Jimmuh Cahtaah debacle and I had no loss of power, the plugs ran really clean, and I had no increased oil consumption from dry cylinder walls.
I believe I was using a Castrol top grade 20-50 oil.
Modified advance curve, full advance possible, big Mallory coil, single Holley 4v, 283ci SB Chevy single exhaust 1960 Chevy convertible with a "demo" suspension/front end/wheels/radials to sell an ultra-luxury ride yet ultimate street handling to the NT high roller crowd whose Caddy, Mercedes, Jags, Lincolns, super-cars were bottoming out a falling apart and turning to junk.
I tried it many years before in HS on a '50 Plymouth convertible using an aluminum war surplus canteen on my exhaust manifold (dumb kid!) but did not have the small fishtank toys or experience or fuel problem that I did under Carter.
I do not recommend you try this without asking yourself why you should and some experience with distributor advance curve modifications -
Fuel Injection and computer controls add a new ball of wax.
Cost of the water - from the tap - alcohol I used I bought by the gallon at Sears in the paint department. Exactly what alcohol I do not recall.
It did work - at least until I was able to back up to the gas pumps in NYC and skip those crazy gas lines.
Gas station owner had a Mercedes diesel and uses the heating fuel he sold for residences and businesses.
NYC was full of station owners that were adding water right into their underground tanks - lines were miles long in NYC.
Jimmy Carter and the democrats - what a scam!
We solved that thru cutting drilling in the USA and conservation right?