Apparently above 100 mg/L... however I must confess I did not try it myself ;-)
This topic now is something else: eutrophication. All live organisms need phosphate (for cell walls, DNA, etc.) and nitrogen (for proteins, etc.). (Plus I need some wine as well) Once you remove one of them, they cannot grow. So eutrophication (nice green colour caused by algae in lakes or the swimming pool) can be controlled by eliminating P, which, as you say, is easier.
Sometimes a little nitrate is actually useful: In wastewater treatment plants around the Potomac river treatment went to such high levels that there was no nitrate left in the river. This sounds good until there is some organic pollution which uses up the oxygen at the bottom of the river. After the O2 is gone (which is not a good situation already), nitrate can be used by bugs to remove the pollution. If there is no nitrate, anaerobic reactions start, i.e. the river starts stinking (H2S).
Yes agreed potential problems but throughout the EU we are not showing an increase in baby problems with higher nitrates so at what point is it a problem any studies into the issue?
Very interesting Imre, what about algae, they can live on nitrates and of course bacteria and others can live on them, while we try to limit phosphates in swimming pools nitrates are harder to eradicate, you thoughts?
BPA is a carcinogen. Nitrate is not. After reduction to nitrite it binds to hemoglobin and babies don't get enough oxygen - two totally different problems. Both are problems, though.
No doubt as nitrates are present due to the natural biodegridation process, the levels maybe of interest to us but are there any studies showing increased cases of cancer? the EPA level maybe much lower but babies are born without an alarming increase in blue baby syndrome throughout the EU as a whole.
I am sorry Geof, but there are no higher organisms that can "live on" nitrate. Only bacteria have the necessary enzyme systems and electron transport chain. Flukes or more typically E.coli is a sign of sewage intrusion into the water table, completely different from fertilizers (which may lead to high nitrate in the well water).
Water with high nitrate content is safe for showering. If it contains E.coli it is unsafe for anything - look for "Walkerton tragedy" on Google.
Your findings may imply a link between the two, which is plausible - around farms they use a lot of fertilizer (i.e. nitrate), and the cowpies on the pasture are the source of E.coli - so around farms both may happen. But flukes do not live on nitrate.
Concerning "phenol and benzene lining their urinary tracts" you must be thinking of BPA (bisphenol-A), BBP (benzyl butyl phthalate) and DEHA (Diethylhydroxylamine). There is truly some chemical stuff in plastic bottles, though BPA is phased out everywhere and DEHA was recently removed from the list of carcinogens. However, I agree, paying a 1000 times more for water is a strange idea (in places where tap water is safe, which is 99.99% in France).
Imre, the water guy.
Of all the water I have tested in the Dordogne I have always found nitrates, but alarmingly parasites that live on the nitrates. The worst ones being the flukes which can trigger cancer, sheeps liver fluke and schistisoma which goes through the blood and uninery tract especially with children that drink a lot of soft drinks from plastic bottles and have phenol and benzene lining their uninery tract. It may change from area to area as I have only tested around the Bergerac to Bordeaux area. Most water I would not even shower in. Mains water may sometimes smell of chlorine but at least is safe especially if it is put through a wellness filtration system. I use a German Rayonex machine for accurate testing of water and there are Rayonex operators around France that can test it.
Amazing... the European limit is 5 times the US limit. Both consider babies as well.
up to 50mg/L is the maximum in french tap water.
10 mg/L is the EPA limit in the US for nitrates.
Excess nitrates isn't particularly hepful, how much of an excess an actual figure and those for the remainder of the test would be useful. With well water the levels change quite regualarly with the seasons and the rainfall. What are you wanting to do with the well water?
Nitrate is coming from fertilizers. The water can be still used but careful with drinking, especially dangerous for babies (blue baby syndrome).
It has most likely been contaminated by the overenthusiastic use of nitrate based fertlisers by the local farmers or by run off from farming muck heaps.Certainly not for drinking or cooking but safe for other uses.