Water is just water, right? What happened when Sierra Madre, a suburb northeast of Los Angeles, switched from local groundwater to imported Colorado River water is a reminder that, well, no:

In 2013, Sierra Madre was forced to begin importing water from the Metropolitan Water District. That led to a new problem. The water source has a different chemistry, temperature and disinfecting agent than the groundwater supply. That started taking a toll on the city’s aging infrastructure.

Residents began to see yellow, foul-smelling water coming from their taps ? the result of iron oxide being released from the inside of old pipes.

When water pipes acclimated to water of a certain pH suddenly get water of a different pH, the chemistry of degunking the inside of the pipes can be a bit of a mess. This is what happened in in the early 1990s when Tucson made a similar switch, as Mitch Basefsky wrote some years ago in Southwest Hydrology (pdf):

Almost immediately following the initial delivery of Colorado River water, the utility began receiving complaints about water that was discolored, smelly, foultasting, or contained rust. Analyses showed that the water contained high levels of iron and other corrosion byproducts from metallic water mains and private plumbing. In essence, the aggressive water was releasing existing corrosion and scale from the pipe walls.