“Do we know what’s in the water we drink?” Using this question as a starting point on the occasion of World Water Day, we interviewed on Facebook Live Cristina Villanueva, head of ISGlobal’s Water Pollution Programme, who talked about the health effects of the contaminants found in water. The following is a summary of the conversation.
Hemos analizado especialmente la exposición durante el embarazo y también los efectos respiratorios en las piscinas
What lines of work are you pursuing in the ISGlobal Water Pollution programme?
Basically, we are investigating the relationship between water pollutants and health. We have focused on the pollutants people are most exposed to because they are the ones that could have the greatest affect on us, such as water disinfection by-products. We wanted to study these compounds because they are a group of pollutants found in all treated drinking water so everybody is exposed to them. We have also studied nitrate, another common contaminant found in our drinking water. In particular, we have studied exposure during pregnancy and also the respiratory effects of contaminants in swimming pools.
With respect to the health impacts of the water we drink, we have heard talk about cancer, reproductive disorders, respiratory problems, and so on. Should we be worried?
That is precisely why we are doing the research: to find out whether or not we should be worried. The subject does raise concerns, which is why it is being investigated. However, that does not necessarily mean that you should be worried.
What are these disinfection by-products present in drinking water?
They are chemical compounds that form when a disinfectant (usually chlorine) interacts with organic matter present in the water. There is no doubt whatsoever that chlorination has been a significant public health advance; drinking water has to be disinfected to prevent disease. But there are collateral effects because disinfection gives rise to the formation of unwanted by-products. Researchers are now investigating whether these compounds affect our health.
One of the peculiarities of the process is that hundreds of compounds are formed: some are volatile and can be inhaled, others are not, and some are skin permeable. Since there is enormous variety in the by-products that are formed there can also be a wide range of health effects. In addition, there are several routes of exposure: inhalation, absorption through the skin, and ingestion.
Initial research appeared to indicate that there might be a health risk, but more recent studies, including those by ISGlobal, have concluded that there are no negative effects.
Unos de los efectos más consistentemente asociados con la exposición a los trihalometanos durante muchos años es el riesgo de cáncer de vejiga
What do we know about disinfection by-products?
The first disinfection by-products identified in drinking water were the trihalomethanes in 1974. Since then, many different compounds have been studied, and the possible association with cancer has been investigated. One of the health effects most consistently associated with long-term exposure (over many years) to these compounds is an increase in the risk of bladder cancer.
Researchers have also investigated links with other malignancies, such as colorectal and breast cancer, but in those cases the evidence is much less consistent. The effects of exposure during pregnancy are also being studied. While the evidence is unclear, there is some consistency in the findings on intrauterine development: a weak association with low birth weight has been reported.
In the case of respiratory effects, the results of observational studies in children who used swimming pools from a very early age gave rise to alarm about the possibility of such exposure triggering childhood asthma. Once again, the initial studies indicated a possible association, which has since been ruled out by more recent research. In fact, our findings at ISGlobal indicate that, on the contrary, infant swimming may have a beneficial effect on children’s pulmonary and respiratory function.
So, your message overall is that we should not be worried, but we should be prudent?
Yes, exactly. It might be better if these chemicals were not present in our water, but it is certainly better to disinfect water rather than not to do so. However, there is a clear association with bladder cancer. So we should be careful about some effects, but with respect to others it would appear that there is not much cause for concern.
El agua se impregna de todo lo que hay en el ambiente en el que circula. Por tanto, puede contener muchas sustancias
We think of water as being just H2O. But what else is in the water we drink?
Water from natural sources is never pure H2O. In fact, water is impregnated by everything found in the environment where it circulates. So, it can contain many substances. And some of them can even have positive health effects. Not all the effects are negative. Some contaminants are regulated and others—called emergent contaminants—are not monitored. For example, analysis of water in rivers destined for use as drinking has identified residues of many products used by humans, such as medicines, cosmetics, sunscreens, and so on.
Earlier you mentioned that you are also studying another compound: nitrate. Could you explain a bit more about that line of work?
The main sources of the nitrate found in water are agricultural fertilisers. Rain water causes them to leach into groundwater and rivers. Nitrate is also associated with intensive livestock farming because it is present in the animal waste products that often contaminate groundwater. Domestic use is another, much less important, source of nitrate. Nitrogen is also an element found in nature. What has happened is that we have altered the natural nitrogen cycle.
And what do we know about the possible consequences of nitrate on human health?
Nitrate itself is not a problem, but it is reduced to nitrite by the bacteria in our mouths. One of the most commonly reported problems is a disorder called metahaemoglobinemia or blue baby syndrome: the nitrite interferes with the oxygen-carrying capacity of the blood, leading to a kind of suffocation. This disorder has been seen mostly in children fed on formula milk made with water containing high levels of nitrate. Nitrate intake also generates nitrosamines, which have been shown in laboratory experiments to cause cancer. Legislation regulating drinking water ensures that they do not reach these high levels, but the question remains whether lifetime exposure at lower levels can be carcinogenic. This is a question researchers are still working on.
El agua del grifo debe cumplir una normativa estricta y podemos, por tanto, beberla con una cierta tranquilidad
What water should we drink? Is filtered tap water the best option? (Yolanda Surriel)
That is a common question, and I am not really in a position to make a recommendation because there is insufficient evidence to support one. Tap water has to meet strict standards, which means we can drink it with some confidence. The standards for bottled water, on the other hand, are much more lax. Producers of bottled water are not obliged to monitor anywhere near the same number of chemical compounds as are monitored in tap water.
And we know very little about filters. We do know that they reduce the content of some contaminants, but they may also reduce our exposure to compounds that may have positive health effects. For example, hard water has been associated for many years with protection from cardiovascular disease. So, they are not all bad for us. We do not yet know whether drinking very demineralised water is a good thing or not. Demineralisation also affects the taste of the water. It is a personal choice. Bottled water also generates an enormous amount of plastic waste. Therefore we have to ask ourselves whether we want to contribute to this serious environmental impact.
A nivel de la salud del planeta, el agua embotellada tiene un gran impacto: generación de residuos plásticos, CO2 en el transporte...
So drinking bottled water does not rule out exposure to contaminants?
Drinking bottled water could mean that you are not ingesting contaminants but, in fact, ingestion is the route of least exposure. Exposure to contaminants absorbed through the skin or via the nose could be much more serious because they go directly into the bloodstream.
In some parts of Spain we found lower levels of nitrate in tap water than in bottled water. But in both cases I am talking about low levels that are not actually a cause for concern.
And, bottled water has a major impact on the health of the planet because of the CO2 generated by its transportation and the plastic waste produced. So we need to take the environment into consideration in any decision on whether or not we should be drinking bottled water or tap water.
It is difficult to buy bottled water that is not stored in plastic containers. Does the plastic bottle have health implications?
Research has shown that components of the plastic can migrate into the water under extreme conditions (heat, high temperatures, exposure, etc.). Nevertheless, there is very little evidence that this contamination has any impact on human health so I do not think that it is a cause for concern.
The quality of tap water is not the same everywhere. What does it depend on? (Isa Otero)
The main determinants of quality are the characteristics of the water before it is treated. The water supplied in the Barcelona Metropolitan Area comes mainly from rivers and reservoirs. The quality of the water varies from one source to another. Water from the Llobregat river is not the same as water from the Ter. The better the quality of the water in the source environment, the better the quality of the water that will come out of our taps. Another factor influencing quality is the method used to treat the water.
In this respect, there are considerable differences between cities. For example, in Madrid and in the north of Spain there is much more water available and the quality is better. In Catalonia, where the climate is dry, we don’t have so much water and we have to reuse it more.
Desde el 2010, el agua de Barcelona ha mejorado mucho en relación a los trihalometanos y, en general, a los subproductos de la desinfección
Can we drink the tap water in Barcelona without cause for concern? (Isa Otero)
Since 2010, there have been substantial improvements in trihalomethane content and in disinfection by-products in general. The treatment plants had to make changes to comply with new legislation. It is always risky to generalise because there are old buildings in Barcelona that have lead pipes, another factor that can influence water quality, but in principle we can say that tap water in Barcelona is safe. The Barcelona Public Health Agency monitors the supply and citizens can ask them to analyse the water in their homes if the building still has lead pipes. Lead is known to be neurotoxic.
Your research into water in swimming pools had worldwide impact. Can you tell us a bit more about it?
We did the field work in 2007. We chose swimming pools because they are associated with a high level of exposure to trihalomethanes and to disinfection by-products in general because of the constant addition of organic matter coming from the swimmers (urine, sweat, hair, cosmetic residues, etc.).
We concluded that swimming in pools altered genotoxic and respiratory biomarkers, although the effects are reversible.
Later, we did a larger study and found no negative health effects. We think that the change in the result reflects an improvement in the quality of the water throughout the whole system in Barcelona. The findings of the second study were good news for public health.
And, finally, a more personal question. What kind of water do you drink?
At home, I drink filtered tap water ...
Thank you, Cristina! We will be back next month with another Facebook Live session.