Looks
A change in your water’s appearance may be the first observable flaw in your drinking water system. Depending on the color of the water, a change in appearance can be an indicator of a vulnerability in your water system.
Changes in color often depend on your water's source and if you are on a public or private system. For public systems, which often gather water from lakes and rivers, changes in color are often a result decaying organic matter, such as leaves buried along a river or lake bed. For private systems, which often draw water from the aquifers in the ground, changes in color are often a result of dissolved metals, such as iron. These metals often stem from the weathering of old piping.
While a simple change of color is not considered a toxic characteristic of water quality, there are toxins that may affect the color and appearance of your drinking water.
IF YOUR WATER LOOKS...
Milky
Dissolved carbonates (limestone, chalk, marble, etc.), excessive air, suspended particles.
Blackish
Iron and manganese reactions, iron-related, slime, bacteria, anaerobic bacteria.
Yellowish
Biodegraded material (peat, plants, soil, etc.), iron, iron-related bacteria, anaerobic/aerobic bacteria.
Reddish
Dissolved iron, iron-related bacteria, anaerobic/aerobic bacteria.
Foamy
Surfactants - Foaming Agents (ex. firefighting foam)