From Where The Water Goes: Life and Death Along the Colorado River by David Owen - -
"Still, the long-term consequences of efficiency improvements of all kinds depend on what happens to the savings. Running a kitchen faucet or flushing a toilet in a municipality with a modern sewage-treatment system is mostly non-consumptive, because the wastewater is treated and used again. Watering a lawn, in contrast, is almost entirely consumptive, because as far as the municipality is concerned that water disappears as soon as it hits the ground. Popular conservation schemes can sometimes merely substitute consumptive uses for non-consumptive ones. Imagine a municipality with so-called block, or tiered, water rates, which are kept low below some threshold, to make ordinary household use affordable, and then rise dramatically to discourage people from casually doing things like washing cars and watering grass. If residents of that municipality now install bathroom and kitchen fixtures that use less water, they shrink their non-consumptive use - by reducing their wastewater return flows back into the system - while simultaneously making watering their lawns and washing their car more affordable since now they can do it with cheaper water. They're using water more efficiently, because they're receiving more value from every gallon; but they've shrunk the available supply of the local water system. The same efficiency efforts can cause operational problems for municipal sewage-treatment facilities, which require volume and dilution in order to function properly. In 2015, prompted by the drought, Californians were remarkably successful at cutting domestic water use, but an unanticipated consequence in many cities are clogging, corrosion, intrusion by tree roots, and other damage within those cities' waste systems, which were not designed to function without big flows to keep everything moving. These are problems that can be overcome, but overcoming them costs money. Conservation increases a municipality's per-gallon cost of financing, building, and maintaining the infrastructure that moves water in both directions, consumers inevitably complain if their bills go up as their consumption goes down."