top of page

Disinfection Byproducts in Drinking Water

Updated: Mar 18, 2022

Victor Luca, 24-Dec-21

Figure 1.(a) conventional single stage point-of-use bench-top water filter system, (b) under-bench system with ion-exchange resin cartridge, (c) enlarged view of ion-exchange resin, (d) sophisticated multi-stage wall-mounted or under-bench system, (e) espresso coffee machine fitted with water filters.

Prior to returning home to NZ, one of the research areas that I had been involved in for more than two decades was the development of materials and methods for the removal of radioactive and non-radioactive heavy metal contaminants from aqueous solutions. In other words, the development of novel technologies for water decontamination.

Many people seem to think that pure water is abundant and comes free. Unfortunately, that is far from the truth. As I have written many times in this newspaper, there is actually relatively little fresh water on our planet, although we in NZ are quite lucky in having more than most countries.

As human activities intensify and climate change bites, the challenges in water provision to communities is expected to become more challenging.

Whakatāne and Ohope get their water from the Whakatāne river. The river water is not clean since the river passes through built-up areas and farmland prior to reaching the Valley Road Water Treatment Plant. At the treatment plant the river water has to be subjected to quite a complex but standard industrial-scale process to remove sediments, nutrients (phosphorus, nitrogen …), metallic elements and pathogens including viruses, bacteria and protozoa (bugs). This involves adding chemicals and applying a range of chemical processes.

Taneatua, Waimana, Ruatoki, Te Mahoe and Matata all get their source water from shallow bores and surface springs. Edgecumbe gets its water from the Rangitaiki Plains rural scheme which involves relatively deep aquifers. Generally speaking, since surface waters are prone to contamination from human activities, water from aquifers is relatively clean compared Whakatāne river water. The majority of the nominated water schemes involve the use of chlorine as a method of disinfection. Disinfection through chlorination is usually the final stage of the water treatment process and is very similar to what is done in a swimming pool. This disinfection method is relatively cheap and has the advantage that the chlorine lingers in the distribution network (pipes) and therefore can continue to disinfect the water until it comes out of your tap.

Chlorine-based disinfection efficiently destroys natural organic matter, pesticides and pathogens. However, the decomposition of these organic materials by chlorine generates a wide range of chemicals collectively known as disinfection byproducts (DBPs). Recent research shows that depending on the organics present in the source water, more than 700 DBPs can be formed. Their concentrations in the finished water will depend on the nature and concentration of the organics present in the source water. Although lots of research is going on in this area, there remain many knowledge gaps.

For instance, we know very little about the toxicology of the majority of the DBPs that have been identified in drinking water. Of the few DBPs we do have toxicology information on, a bunch are known to be carcinogenic. For instance, studies have shown that the chances of bladder cancer resulting from the sustained drinking of chlorinated water is increased by about 50%. The more organic impurities in the source water, the more chlorine you have to add and the higher the concentration of DBPs.

So here’s the thing. If we didn’t chlorinate we would run significant risks of acute health effects, viz gastrointestinal illness such as what occurred in Havelock North in 2016. If on the other hand, we do chlorinate, we reduce the risks of acute effects but increase those of chronic effects like bladder and other cancers.

Many will now be aware that the Government is reforming the 3-waters system. By 3-waters we mean drinking water, storm water and waste water. The forth water, which is not in good shape either, is water in rivers, lakes and aquifers; the source water. More than 40% of NZ lakes suffer from eutrophication caused principally by increased nutrient load from intense agriculture. For drinking water, it appears the new water regulator (Taumata Arowai) will try to enforce chlorination more generally in New Zealand since it removes the risk of acute effects. This doesn’t mean the water is of high quality since we are essentially playing acute effects off against chronic effects.

It should be noted that there are other methods of disinfecting water including ozone treatment, ultraviolet irradiation, the use of nano-filtration membrane systems and so forth that are beyond the scope of this article. None of the available disinfection methods is perfect, each has its pros and cons. It is all about risk compromises.

As part of the government’s 3-waters reforms, a new regulator, Taumata Arowai, has been formed. The regulator’s job is to monitor and enforce standards. Drinking water standards are all about setting maximum allowable values (MAV) of pathogens, organic compounds, inorganic and radioactive elements. The new regulator has not made any significant changes to the existing standards, in fact they have relaxed some of the MAVs. However, we can assume that they will take their monitoring and enforcement role more seriously than the Regional Council was able to do under the previous legislation.

It is important to emphasize that the reforms will not change the MAVs for a particular water scheme it will only enforce them more widely. What this means is that the compliant water we are presently getting in the district at the moment will not improve further in quality because the MAVs will not change. So when the dust settles on these water reforms, nothing will have changed for most of us as far as drinking water quality is concerned.

I have corresponded with Taumata Arowai to ascertain what their attitude will be toward the DBPs. At the moment they will only monitor about half a dozen or so of the more than 700 DBPs in our drinking water. Their rationale for monitoring only a handful of DBPs is that these will give an indication of the content of other DBPs. This is not necessarily so since we know nothing of the toxicology of the vast majority of DBPs, and in any case, we don’t know the distribution of these compounds at time of treatment let alone how they evolve over time as they travel down the distribution network.

It is hard to avoid chlorination if we want to avoid acute health effects in our communities but the possibility of longer term effects is also hard to deny.

Since most of the water the treatment plant produces is used for flushing toilets, showering, gardening and washing cars and boats, I would recommend the use of a point-of-use (POU) bench-top or under-bench filter system. Not all filters are created equal however.

Single-stage bench-top filter systems (Figure 1a) containing activated carbon filter cartridges or combination activated carbon and ion exchange resin cartridges can remove up to 70% of DBPs and some heavy metals. They cost as little as $60 and require no installation. More sophisticated multistage systems with a reverse osmosis stage (Figure 1d) can be purchased for somewhere between $300 and $500 and they produce very pure water. However, they require more space and are somewhat more difficult to maintain. They are even capable of removing fluoride for those that are worried about this. Failure to maintain a filtration system properly and replace filter elements when needed can cause more problems that it fixes. As time evolves these systems are bound to become cheaper and smarter.

I would continue to advise the use of POU filter systems, no matter what the reforms end up looking like.

Again I have to emphasize that most important of all is the protection of our source water, because the best water of all is the water that doesn’t need cleaning because nature has already done the job.


[1] Diana, M., Felipe-Sotelo, M., Bond, T. Disinfection byproducts potentially responsible for the association between chlorinated drinking water and bladder cancer: A review. Water Research 2019, 162(492), e504.

[2] Verburg, P., Hamill, K., Unwin, M., Abell, J. Lake water quality in New Zealand 2010: Status and trends. NIWA Client Report: HAM2010-107. August 2010. NIWA Project: OIC10202.

[3] Wu, J., Cao, M., Tong, D. et al. A critical review of point-of-use drinking water treatment in the United States. npj Clean Water 2021,4, 40.

[4] Villanueva, C.M., Fernández, F., Malats, N., Grimalt, J.O., Kogevinas, M. Meta-analysis of studies on individual consumption of chlorinated drinking water and bladder cancer. J. Epidemiol. Community Health 2003, 57(3), 166-73.

27 views0 comments


bottom of page