Reference

What a water test actually measures.

One page per thing a lab reports. Each says what it is, what it usually does, what a result does not prove, and when it is usually worth testing. None of them tells you what is in your water. That is what the exam and a lab are for.

• hardnessHardness is dissolved calcium and magnesium.
• ironIron comes in two forms, and the form usually matters more than the amount.
• manganeseManganese is the one that usually stains black.
• pHpH is the acidity scale, and the low end usually eats copper.
• hydrogen sulfideHydrogen sulfide is the gas behind a rotten egg smell.
• iron bacteriaIron bacteria are alive, which is why they come back.
• tanninsTannins are dissolved, which is why straining does nothing.
• TDSTDS is a total, not an ingredient list.
• chlorineChlorine is added on purpose, and it is supposed to still be there.
• arsenicArsenic has no taste, no smell, and no color.
• leadLead usually comes from the pipe, not from the water source.
• nitrateNitrate is the one that usually arrives from the surface.