Water By Clara Lu — Date 11.23.2018

What goes on in municipal water treatment plants, and where it ends

The full process can seem impenetrable to users. To that end, here’s how a general municipal drinking water facility works, and how it fails to completely purify your water.

The latest report published by the WHO/UNICEF Joint Monitoring Program for Water Supply, Sanitation and Hygiene shows that in 2015, 75% of the global population (5.2 billion people) used a safely managed drinking water service; one that is located on premises, available when needed, and free from contamination.

In most countries – especially developed nations – many equate this drinking water service to tap water. It belongs to a system that is regulated by global, state, and federal agencies, such as the World Health Organization (WHO) or the United States Environmental Protection Agency (EPA).

The water that comes out of our taps starts off as rain. This rainwater is collected in reservoirs via rivers and streams or filters through the earth to form groundwater. However, these drinking water sources are subject to contamination and need to be treated because it’s clean enough for human consumption.

Water companies then pump this raw water to their water treatment works, where it goes through treatment processes to remove pollutants and disease-causing agents. Substances that are removed during the process of include suspended solids, bacteria, viruses, organic and inorganic contaminants, and also macro and micro mineral nutrients such as calcium, iron and manganese.

The following are the most common processes used for municipal drinking water treatment:

 

1. Filtration

The water travels through large filters made of sand, gravel, and charcoal to remove the remaining dissolved particles such as dust, parasites, bacteria, viruses, and chemicals.

Rapid sand filters are often used, where water moves vertically through sand that has a layer of activated carbon or anthracite coal above it. The top layer removes organic compounds, while remaining suspended particles get trapped in pore spaces or adhere to sand particles.

Slow sand filters may be used where there is sufficient land and space, and relies on biological treatment processes rather than physical filtration. The filters are carefully constructed using graded layers of sand, with the coarsest sand at the bottom and finest sand at the top. Filtration depends on the thin biological layer (or biofilm) on the surface of the filter, which provides effective purification by absorbing and metabolizing contaminants.

 

2. Disinfection

Most drinking water treatment plants also take on a multi-barrier approach to further reduce the contamination of drinking water from source to tap. This system allows the water to be treated with more than one disinfection method, including using disinfectants such as chlorine, ozone, ultraviolet radiation, carbon and ion exchange, or reverse osmosis to remove microscopic and dissolved particles from the water.

At the minimum, chlorine or chloramine (a combination of chlorine and ammonia) is added to disinfect the water. This is a popular method because residual chlorine remains in the water all the way through the distribution system, protecting it from any microorganisms until the water reaches the consumers. However, this also means that people who are more sensitive than others to the smell or taste of chlorine may become aware of occasional changes in chlorine levels in their tap water.

 

3. Supplementary treatment

Supplementary treatment may sometimes be needed for the benefit of the population. One such instance is the fluoridation of water, where fluoride is added to water. The WHO states that ‘fluoridation of water supplies, where possible, is the most effective public health measure for the prevention of dental decay’.

After treatment, the water is then pumped into pipes that deliver it to homes and businesses in the region.

From the lake to the tap, the purification steps that tap water goes through are crucial and require constant monitoring. Yet, if you think that this process is foolproof and impeccable, you might be disappointed. The municipal water treatment process, however stringent and guarded, is one that is easily threatened by bacterial outbreaks, natural disasters, poor infrastructure, oversight, and human activity.

 

Loopholes in the drinking water treatment process

Contaminants can still be found in tap water even after treatment. In fact, 316 contaminants – including industrial solvents, weed killers, refrigerants and the rocket fuel component perchlorate – have been detected in the tap water of 45 American states during a three-year study. Out of which, approximately 200 of them are unregulated, including:

  • 97 agricultural pollutants such as pesticides and fertilizers
  • 204 industrial chemicals from factory discharges and consumer products
  • 86 contaminants linked to urban areas, polluted runoffs, and wastewater treatment plants
  • 42 pollutants that are byproducts of the drinking water treatment process or from old pipes and storage tanks

 

Regulatory limits

According to the study, the EPA regulates the rest 114 of these pollutants, setting maximum legal levels that water utilities achieved 92% of the time. The remaining chemicals, which have no mandatory federal safety standards, can come in potentially toxic combinations for long-term consumption.

For instance, the EPA’s legal limit for atrazine,the second-most common herbicide used in the U.S., is three parts per billion in drinking water. The EPA data show that last year, water utilities in Illinois, Kansas, Kentucky, and Ohio had atrazine spikes much higher than the federal legal limit for the chemical – up to 22 parts per billion. Yet the Safe Drinking Water Act allows utilities to report only annual averages of testing for the chemical, keeping them under the legal limit but masking the presence of the atrazine spikes. Some of the utilities with elevated levels do not even test for atrazine during periods of spikes.

The water that comes out of your tap may be legal, but it isn’t the same as being free of contaminants. It certainly raises some health concerns. At the moment, it’s a matter of keeping it out of sight and out of mind for regulatory bodies. If the contaminants are not regulated, there are also no standards or checks done to test their presence in our water supply. As a result, defenses and treatment methods to eliminate them from the water are also lacking in the system.

 

Treatment method limitations

Usually, disinfectants and their byproducts are released into the water the last treatment step before it is supplied to users. This means that there is no way to completely remove these purification agents before it reaches the household.

Current methods and systems also have limitations on the extent to which they purify water; they remove “common contaminants” that are regulated by the law, but are ineffective against the more tricky pollutants such as pharmaceuticals and microplastics. It is extremely costly and in some places, the technology required to do the task is not readily available for application.

 

Old delivery pipes

As water passes through the distribution system, its quality can degrade via chemical reactions and biological processes. Corrosion of metal pipe materials in the distribution system can cause the release of metals into the water with undesirable aesthetic and health effects.

As such, lead pipes or fittings were the culprits in the water crises in Flint, Baltimore and other cities. Lead pipes were known to be a risk by the 1700s, but they were widely installed in many countries until the mid-twentieth century. When pipes age and corrode over time, there is an increased risk in lead leaching from the pipe surface into drinking water.

 

Your fixtures, your problem

Furthermore, the water line from the street to the home, and the plumbing within your home, may also be in bad shape or contains lead, but those fixtures belong to the property owner, not the utility. Tap water quality is only guaranteed by regulatory bodies until home water meters, after that, it is the user’s responsibility.

These factors potentially reintroduce harmful contaminants back into your water before it flows out of your tap, and drinking it leaves too many variables to chance. To gain awareness on the quality of your tap and drinking water, it’s best to test it for contamination.

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