The process of achieving a sustainable and equitable rate structure for fresh water and waste water treatment depends on population, water source, previous approach to pricing, types of users and amounts used and whether the municipality manages water and sewer treatment has a separate or combined enterprise fund.
Rural areas have the toughest row to hoe simply because there are not many residents and commercial users to foot the bill.
If the cash flow model is 20-years, this suggests an area that is not growing with declining revenues and capital reserve fund. This background is usually associated with municipalities with aging systems that did not charge customers for actual cost of service.
I live in Pinellas County, Florida – over 3,000 people per square mile.
Our population is declining, property values dropped by 40 to 50 percent (less tax revenue), unemployment is high (many “undocumented workers” have left due to lack of work), lots of business closures, etc.
Our main problem is water not treatment – our aquifer was essentially destroyed years ago by mismanagement and overuse and now we have to buy water from other areas at a great distance meaning significant increased cost.
In your case, planning out 20-years was mostly likely out of necessity to avoid significant rate shock to residents who are minimal users with less resources at hand in relation to commercial users.
Of course, other carwash operators are on board for lower rates, who wouldn’t?
However, in a rural area, when push comes to shove, I doubt there will be much sympathy from the general public when you ask for rate adjustment when they have no such recourse.
As Dean mentioned, a possible solution would be reclaim as well as conservation measures plus passing cost to customers.
Good luck.