I only bring this up to reinforce your understanding that the city water supply is not necessarily clean and reliable, just because the water has passed through a complex system designed to make it fit to drink. Knowing this, we have installed a compact filter system on our faucet at home, and all water that is to be used for food preparation or drinking is taken from that filter.
An alternative is to buy bottled water, but I am not entirely confident that the bottler of that water can guarantee purity any more than the city water utility can. Accidents can happen. Equipment can fail. And contaminated water can sneak through the system. So we prefer to filter our own at home.
There are various causes for a community water supply to suffer damage, allowing contaminants into the water lines. This can happen during an earthquake, a severe winter freeze, a flood, a water treatment equipment failure, a sewage treatment equipment failure, or when excavation equipment accidentally breaches a pipeline. And that doesn't even take into consideration an intentional attack on the water supply by terrorists.
Tomorrow we'll talk about boil orders, what that means and how to handle it.