Actually tankers are not cost-viable today (and probably never will be).
A friend of mine and I (both marine engineering professionals in commercial shipping) did a Cost Benefit Analysis on chartering a handy size tanker, cleaning the tanks and shipping water from Alaska to California during the droubt. I no longer have the email that broke the costs down, but cleaning costs aside, the operational costs alone yielded $0.25/gal. The cost of H20 in Ca is about $0.002/gal (cheaper for farmers).
If you're looking to start an H20 ptoduction venture, you need to account for demand factors that will inform the type of product that is needed. For example, if the demand is geographically fragmented and/or geopolitical isolated (e.g. to remote villages in relatively undeveloped or oppressive nations) then a small and very cheap personal H20 generation technology is probably more cost feasible than creating a supply infrastructure.
Just calculate the cost/galon at the end user then compare to today's cost and you'll have your answer.
I think tankers will still work, but the problem has to be attacked from a different angle.
California's water is a repayment on the bond measure for building it's infrastructure back in the 60s. It's somewhere around 80% of the price of water. This is the largest reason for it's seemingly fixed cost and relative cheapness, even during the drought years. Under these circumstances a single tanker is simply a drop in the proverbial bucket.
What California's drought hurts is the entire state's total water carrying capacity year over year. Once that reaches a critical low, California will be spurred to take another water bond project of equal size. I predict this will fund desalinization plants along the coast.
Looking at the problem from this perspective, I'm estimating how much water is produced daily by a given plant. The question then becomes "Can I produce as much water as this plant for less money (loan/maintenance/electricity)?" I imagine this requires a dozen such tankers each day in Los Angeles harbor, each selling at half the cost per gallon.
Now this might be impossible to engineer cost wise because of the very math you mentioned. It also requires a staggering amount of water production, which itself might be impossible. The logistics of managing such an enterprise might crush the venture under it's weight. I'm still working through these assumptions.
Still, you've helped greatly because now I know the current cost to maintain a tanker. It's expensive, but that's a number I can attack to drive down.
I was imprecise. As long as the tanker was filled greater than 95% of capacity with OJ concentrate, that's ok. Shippers aren't in the habit of leaving oil in the tank -- regulations only require rinsing/cleaning for residue in some situations.
It's buried in the CFR somewhere for the Motor Carrier Safety Administration.
I use, on average, about 3 litres of gasoline a day and about 250 litres of fresh water. This doesn't include the water used to grow the food I eat and it doesn't include the fuel to bring me my food.
But there is a difference of about two orders of magnitude.
