Cleaning Water, Step by Step

After listening to and reading India’s blog post about water pollution, I decided to further investigate the methods used to clean the water we drink and bathe with. Covered in her blog post, she mentioned pollutants within the water such as bacteria, chlorine, nitrates, and heavy metals. With all these particles and microbial life swimming in our tap water, it’s a miracle we aren’t ridden with diseases. I began to wonder, what do private firms and the government do to remove and minimize all these pollutants?

Huangpu River Pollution
Huangpu River Pollution

So I began my search on the companies who clean Shanghai’s water supply. Veolia Water is one of the major companies who purify and distribute water to households around Pudong. Veolia first extracts their water from underground aquifers and surface water bodies. These areas are protected to prevent pollution. All the water then passes through a purification process, which includes coarse and fine screening, flocculation and settling, filtration, ozonation and chlorination. (Veolia Water, 2010)

Screening is a process in which water is ran through different sized screens to stop rocks and other larger objects from entering the rest of the system. It then moves into a system called flocculation and settlement. Within water, there are usually small clay or dirt particles are suspended, giving water the yellowish, brownish look. These particles are often negatively charged, preventing them from clumping together. Hydrated ammonium alum (NH4Al(SO4)2Ÿ 12H2O) is  added to the water to neutralize the negative charges, allowing particles to combine and form larger particles called flocs. The water passes through a paddle chamber that assist flocculation of particles. The following chamber allows the larger particles to settle due to gravity, removing the majority of the clay. (Drinking Water Treatment – Flocculation, n.d.)

Flocculation of Clay Particles
Flocculation of Clay Particles

After flocculation, water is passed through a gravel and sand filter that removes the remaining clay particles. However, this does not remove metal ions, nitrates, or microbial life from the water. Ozonation, the process of bubbling ozone through water to purify it, is often performed to clean water but is more costly than adding chlorine as a disinfectant. Ozone, O3, is synthesized by the use of UV light or electrical discharges. Bubbling ozone through the water kills microbial life. It also reacts with metal ions such as Iron and Manganese, creating insoluble metal oxides, which can be filtered out. (Oram, n.d.) Unlike ozonation, chlorination is relatively inexpensive and will continue disinfecting after leaving the water purifying plant. Chlorine is added into the water, which kills microbial life; however, it doesn’t remove metallic ions. (Drinking Water Treatment – Disinfection, n.d.)

Once the water leaves the purifying plant, it is transported to households across Shanghai, but chlorine and nitrates still remain within the water. In addition, faulty and leaky pipes allow contamination of minerals and other compounds into the water system.  To combat this, some houses have granulated active carbon filters and water softeners. Water passes through grains of active carbon (organic material or coal treated with heat) to react and trap chlorine and some trihalomethanes (THMs, carcinogens), preventing them from being consumed or absorbed by the skin while bathing. (Water Treatment Using Carbon Filters, 2012)

Water softeners are used to reduce calcium and magnesium ions. Although these metals are not harmful to the body in small amounts, they cause pipes to calcify and clog up, decreasing water pressure. Calcium and magnesium ions are replaced with sodium ions found on the ion exchange resin sites found within the filter. (Skipton, 2008)

Despite all these processes, nitrates still persist within the water. Currently, the only way to remove nitrates would be through reverse osmosis or demineralization, both of which require lots of energy and are expensive to maintain. (Runyan, 2011) Often, some people use faucet filters to further purify the water. These are often carbon filters, which still don’t remove nitrates from the water supply.

With all these methods used to purify the water, it still comes down to the question, is tap water in Shanghai safe to drink? Or is any tap water safe to drink for that matter? Ultimately, it becomes the individual’s decision. How much does one trust the government and others to handle their water? Do the benefits outweigh the cost of purchasing distilled water? Judgment of these crucial matters always lies within the person.


Drinking Water Treatment – Disinfection. (n.d.). Tech Alive Home Page. Retrieved March 25, 2013, from

Drinking Water Treatment – Flocculation. (n.d.). Tech Alive Home Page. Retrieved March 25, 2013, from

Oram, B. (n.d.). Ozone Water Treatment, Ozonation, Ozonator Dirty bad tasting water, contaminated colored water, unfiltered water, bad smelling water. Private Well Owner Drinking Water Pennsylvania Ground Water Research . Retrieved March 25, 2013, from

Runyan, C. (2011). Nitrate in Drinking Water. NMSU: College of Agricultural, Consumer and Environmental Sciences. Retrieved March 25, 2013, from

Skipton, S. (2008, October 8). Drinking Water Treatment – Water Softening (Ion Exchange). NebGuide. Retrieved March 25, 2013, from

Veolia Water | Production and supply of drinking water. (2010). Veolia Water | The world leader in water services and water treatment. Retrieved March 25, 2013, from

Water Treatment Using Carbon Filters (GAC). (2012, August 1). Health State MN. Retrieved March 25, 2013, from

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