How Much Is One Part Per Million (PPM)?

PPM (Parts Per Million) = 1mg/L (1 milligram per liter)
PPB (Parts Per Billion) = 1ug/L (1 microgram per liter)
PPT (Parts Per Trillion) = 1ng/L (1 nanogram per liter)
PPQ (Parts Per Quadrillion) = 1pg/L (1 picogram per liter)

You can think of it this way: 1ppm is a couple of drops of water in a 2 liter soda bottle. 1ppb is a little bit of wetness in the same 2L bottle. 1ppt is imperceptibly damp, and 1ppq is basically bone-dry.

My water utility sent me a statement of contaminant/constituent levels in the drinking water, and there was a page of data and two pages of "don't worry it's all normal" explanation. I realized I had never done these maths but I knew that the levels involved were very small and my utility is looking out for me.

In case you were wondering what some normal water levels might be, here is what we're drinking in my neighborhood, and what is the maximum permissible limit (average reading / MCL). Some stuff doesn't have a max. limit or is unregulated.

Barium: 0.054ppm / 2ppm
Fluoride: 0.96ppm / 4ppm
Nitrate: 0.5ppm / 10ppm
Radium 1.25pCi/L* / 5pCi/L
Chloramine: 1.5ppm / 4ppm
Lead: 3.3ppb / 15ppm
Chloride: 44ppm / 300ppm
Copper: 0.014ppm / 1ppm
Iron: 0.067ppm / 0.3ppm
Manganese: 0.0015ppm / 0.05ppm
Sulfate: 97ppm / 300ppm
Total dissolved solids (TDS): 538ppm / 1000ppm
Zinc: 0.016ppm / 5ppm
Nickel: 0.003ppm
Magnesium: 34PPM
Ph: 6.9
Sodium: 83ppm

*pCi/L = picocuries per liter, a measure of radioactivity

This water is actually pretty clean. You'd be astonished at what comes up straight out of a well!