Phosphatemia—How Green is your Water?

Phosphate in drinking water
Colorimetric phosphate test

My swimming pool has a thin green carpet. The fish and frog pond is choked with weed and slime. Even sugar water in the hummingbird feeder turned cloudy in 24 hours. What’s going on?

Now I’ve lit my pipe let’s start the inquiry, Dr. Watson.  Does the water have a common source? Is it polluted?

Yes and no, Holmes. The water originated from our faucet, but we didn’t spread fertilizer in the garden.

Hmm. Tell me, then, what can make stuff grow quickly in water?  

My dear Holmes, I’m reminded of rapidly growing dead zones in the Bay during summer, though the tides were ‘red’ with algae, never green. But if I have the same problem at home the answer must be phosphate.

Congratulations on your deduction and commiseration with the slimy state of your water. Now give it a test.


A combination of colorimetric and laboratory tests confirmed high levels of phosphate in samples from all three sources, but even higher straight out of the tap people drink from. In excess of 4,000 parts per billion, exceeding the sanitation capacity of free chlorine in the pool. How so, when only <100 ppb from the garden well and rainwater barrel?

Remember Flint, Michigan, in 2014? The city managers (that’s what they call them) switched the water supply to save money. Instead of the Detroit river where phosphate was added they drew from the Flint river which has only a low natural level.

Phosphate is added to domestic water supplies around this country, Britain and others included, to avoid poisoning children in homes that still have lead plumbing. It reduces lead in drinking water by coating pipes. Few people seem to know or ask what’s in their water. Phosphate isn’t mentioned in the James City County Water Quality Report, although plenty about bacteria.

Like other living organisms, bacteria need phosphorus to grow, and some kinds are able to liberate more from insoluble mineral. The municipal answer to lead provides more food (PO4) for bacteria and algae to grow, and that consequence is fixed by pumping more chlorine in our water.

Holmes didn’t seem worried about drinking our local water (or that in Baker’s Street, London). He is glad of a generous helping of phosphate in his diet to top up his hydroxyapatite and ATP reserves, but spurns colas supercharged with phosphoric acid for the sake of his brain.

By Roger Gosden

British-born scientist specializing in reproduction & embryology. Career as professor & research director spanned from Cambridge to Cornell's Weill Medical College in NYC. Married to Lucinda Veeck Gosden, embryologist for the first successful IVF team in America. Retired early to Williamsburg, Virginia, to write and recover from 'nature deficit disorder'. Currently a visiting scholar at William & Mary. https://en.wikipedia.org/wiki/Roger_Gosden

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