Water is usually distributed through city or regional water pipes, where it can also pick up contaminants:
Cracks and Faults
If pipes are old, they may have cracks that can allow external contaminants to make their way into your water.
Some pipe and pipe assembly materials may leach into the water.
It is also possible that cross connections, such as sewage lines that run in close proximity to water lines, may increase the risk of water becoming contaminated.
Storage Tanks and Rooftops
Water is also vulnerable to contamination in rusty storage and rooftop tanks.
Home Pipes or Service Connections
Depending on how old the pipes are, your water may be a danger of contamination from substances, such as lead, as it travels to your faucets.