All about the unique filtration system of Paris
Can you really drink water from taps in Paris? Is it really clean, healthy, and tasty? What is the filtration process used?
Safe and portable water is provided to taps by local water providers like Eau de Paris, which provides safe drinking water to every tap in the metropolitan area. Half of the people consume water that comes from rivers and the other half from underground sources (aquifers) with no impact on the water table.
There are 2 water supply systems in Paris, one for tap water, and another for unfiltered water used for cleaning and flushing. There is no water mixing from the two systems, so drinking water is safe.
Paris tap water is considered safe to drink according to French, EU and international standards (WHO).
Every day at the Eau de Paris, over 200 samples of water, from different sources, undergo research and analysis in laboratories which are divided among different departments like chemical, organic chemistry, bacteriology, and corrosion.
The content of calcium in Paris water is around 80–120 mg/L, which near to the range of hardwater and will cause some limescale. It’s close to some natural mineral waters (that have 80 to 100 mg/l of calcium).
Although Paris’s tap water is safe to drink, there still might be certain risks, such as presence of microplastics, chlorine by-products, lead (quite rare), pesticides or nitrates. These can be specifically harmful in greater amounts. There is also the risk of pipe-corrosion or leaching, but it is not very common.
People in Paris might use water filters to make water taste better (removing the chlorine will make the water taste better instantly), or to make it safer for infants and small children as they are more sensitive.
Bottled water is also available but there is no evidence that bottled water is healthier than tap water.
The Process
Use of UV
An integral sensor monitors the UV light intensity in each treatment chamber. A custom-built control panel provides communication between the UV units and the plant control room. Incorporated in each UV unit is an automatic wiping mechanism that cleans the quartz sleeves surrounding the lamps and keeps them free of waterborne deposits.
UV works by rendering microorganisms to be able to reproduce by irradiating or disrupting their DNA. Microbial DNA generally absorbs UV most effectively at 265 nm, produced in abundance in medium pressure lamps. They emit UV over a very broad range of wavelengths (about 185–400 nm). Research has shown that, with proper pretreatment and a well-maintained UV disinfection system, this broad output causes permanent inactivation of both pathogenic and non-pathogenic microorganisms such as Escherichia coli (E. coli).
Low pressure UV lamps, an alternative to medium pressure lamps, produce just a single peak of UV output at 254 nm. While also having a strong germicidal effect, it has been shown that some microorganisms are able to repair or reactivate themselves after exposure to UV from low pressure lamps, especially if they’re subsequently exposed to sunlight. This is known as photoreactivation.
Permanent damage caused by medium pressure UV can result from the UV at other wavelengths, such as 240 nm and 280 nm, affecting other intracellular molecules such as RNA and enzymes, which are unable to repair themselves.
Two-Pronged Treatment Approach
The state-of-the-art treatment plant in Mérysur- Oise draws water from the Oise that passes through a physical filter (like a screen), to remove larger impurities like branches and plastic bags before entering a 370,000 m³ raw water storage tank reserve to remain for 2–3 days, allowing smaller objects to sink to the bottom.
The water then takes two treatment paths:
1. Membrane filtration
About 70% of the water undergoes membrane filtration system utilizing lamellate decantation, double-layered filtration, microfiltration, nanofiltration and degasification before undergoing UV disinfection. According to the operators, the Méry-sur-Oise plant was the first in the world to use nanofiltration to produce drinking water from surface water.
2. Biological treatment
The remaining, that is 30% of the water, passes through a biological treatment path which utilizes methods like decantation, sand filtration, ozonation, activated carbon filtration and chlorination.
The water treated from the two processes is mixed before being distributed on the network, supplying 37 districts in the northern suburbs of Paris. The operators claim that the two-pronged treatment approach results in exceptionally soft and quality water.
Key Takeaways
Tap water in Paris is safe to drink, tasty, and of high quality; bottled water is healthier than it. The filtration system uses UV technology the most which gives assurance that the water is clear, microbially-free, odorless, and has no unpleasant taste. Further research is still going on to make the process permanent.
