35 °C in the shade, closed shutters, and a bottle of water that never leaves your side. During a heatwave, drinking becomes a reflex. But at the same time, the heat and drought can put water resources under pressure.

Managing your drinking water well during a heatwave does not mean drinking less. You must continue to hydrate sufficiently, while avoiding unnecessary consumption and remaining attentive to the quality of the distributed water. From tap water to drought-related restrictions, here are the right habits to adopt when temperatures climb.

Why does drinking water become an issue during a heatwave?

The first issue directly concerns our bodies. When it is very hot, we sweat more to regulate our temperature. This water loss must be compensated. The Ministry of Health recommends drinking regularly during high heat, without waiting until you are thirsty.

This vigilance applies to everyone, but some people are more vulnerable to the effects of heat. This is particularly the case for the elderly, infants and young children, pregnant women, people with certain chronic illnesses, or those working outdoors. For recommendations adapted to a specific medical situation, it is best to consult a healthcare professional.

But a heatwave often occurs in a second context: drought. High temperatures increase evaporation and the evapotranspiration of plants. When added to a lack of rainfall, river flow rates can decrease, soils dry out, and some groundwater sources may be less well-replenished.

We then find ourselves faced with a paradox: we need more water at a time when the resource may be under greater strain. Human needs increase, agriculture may also require more irrigation, and certain tourist or domestic uses increase during the summer.

It is precisely to prevent the situation from deteriorating that restrictions may be put in place locally. Their goal is not to stop the population from drinking, but to reduce non-priority uses in order to preserve enough water for essential needs.

Can you drink tap water during a heatwave?

Yes, as long as no local health directive states otherwise. An outside temperature of 35 or 40 °C does not automatically make tap water unfit for consumption.

In France, water intended for human consumption is subject to health monitoring. Many microbiological, chemical, and physical parameters are monitored to verify that it meets applicable regulatory requirements.

Heat should therefore not lead to the systematic replacement of tap water with bottled water. However, a particular local situation may lead to temporary recommendations. This can happen, for example, after an incident on the network, a problem affecting a treatment plant, or contamination detected during a check.

In this case, the town hall, the water supplier, or the Regional Health Agency may ask you not to use the water temporarily for certain purposes. These instructions always take precedence over individual habits.

At home, another simple reflex is to use cold tap water for drinking and cooking rather than water from the hot water circuit. This water has stayed in a tank or an interior network at a high temperature and is not intended for the same food-related uses.

After a prolonged absence, for example upon returning from vacation, the water may also have remained for several days in the home's pipes. Letting the cold water run before drinking it allows you to flush out the water that has stagnated in the interior network.

Finally, heat can alter our perception of taste. Water consumed lukewarm is generally less pleasant than cold water. If the taste of your tap water bothers you more in the summer, fill a clean carafe, close it, and place it in the refrigerator. However, avoid keeping it for several days.

Heatwave and drought: saving water without drinking less

This is probably the point that leads to the most confusion. When authorities ask to save water, some may have the impression that they should also reduce the amount they drink. This is obviously not the goal.

Hydration remains an essential need. Savings should focus on uses where there is room for maneuver: watering, washing, swimming pools, leaks, or simply bad daily habits.

At home, a few simple actions can significantly reduce consumption:

• take a shower instead of a bath and avoid prolonging it unnecessarily;
• turn off the tap while brushing your teeth or soaping up;
• run the washing machine and dishwasher when they are full;
• locate and repair leaks quickly;
• limit garden watering and respect the schedules when it remains permitted;
• do not systematically use drinking water when non-potable water can legally be used for the purpose in question.

Drought-related restrictions are decided locally. They are organized around four levels: vigilance, alert, reinforced alert, and crisis. The more worrying the situation becomes, the more significant the limitations are.

Specifically, this may concern the watering of gardens and lawns, the filling or emptying of swimming pools, the washing of vehicles, or certain professional and agricultural uses. The rules can differ from one territory to another, hence the benefit of consulting VigiEau rather than relying on general information seen on social media.

At the crisis level, priority uses are preserved. The supply of drinking water, health, civil safety, and certain essential needs remain at the heart of resource management.

The right reasoning is therefore simple: save water where it can be saved, but do not reduce your hydration to save a few glasses of water.

Can a heatwave affect water quality?

To understand what can change, we must look before the tap. The water we drink comes from a resource: groundwater, river, lake, or reservoir depending on the region. It is then collected, treated, and then sent to consumers.

A prolonged period of heat and drought can alter the characteristics of this resource. When a river's flow decreases, for example, the volume of water available to dilute certain substances also decreases. The water temperature can increase, and the biological balance of the environment can evolve.

In some bodies of water, high temperatures combined with other favorable conditions can also contribute to the development of cyanobacteria. These photosynthetic microorganisms are naturally present in aquatic environments, but certain proliferations can cause problems when they produce toxins.

However, a distinction must be made between raw water and the water that reaches the tap. A variation in the quality of a river or groundwater does not mean that this same variation is automatically found in the distributed water. Production facilities are specifically responsible for treating the water, and their operation can be adapted to the characteristics of the resource.

Health monitoring therefore remains the reference for knowing whether distributed water meets quality requirements. Its appearance alone is not enough: many of the parameters checked are invisible and have neither taste nor smell.

If you wish to understand what can be found in distributed water, our article dedicated to contaminants present in tap water in France details the main families of substances monitored.

An unusual change in color, taste, or smell nevertheless deserves your attention. If in doubt, contact your water supplier or check the health information available for your municipality rather than trying to determine the cause yourself.

Tap water, bottled water, or filtration: what to choose in summer?

When temperatures rise, consuming bottled water may seem reassuring. However, if your network water is declared potable, a heatwave does not require you to switch to bottles.

Tap water even has an obvious practical advantage: it is available directly at home. No heavy packs to carry in 35 °C weather, no dozens of bottles to store, and less packaging waste to manage.

If you use bottled water anyway, pay attention to its storage. Bottles must be kept in a clean, dry place away from prolonged exposure to the sun and heat. The trunk of a car parked in the sun for several days is therefore not a suitable place to keep a water supply.

Another option is to filter network water directly. The goal is different: it is not to make water subject to a health ban drinkable, but to treat the water already distributed at home in order to reduce certain contaminants depending on the technology used, as well as certain tastes and odors.

This approach can be particularly practical for households that usually buy bottles mainly because they do not like the taste of their tap water. It allows you to maintain direct access to water at home without constantly managing packs.

The FLX Compact fits into this logic. Installed on the home's water inlet, it works using network pressure, without electricity or chemicals. It aims to reduce contaminants present in the water as well as bad tastes and odors.

Its operation without electricity also means that a power outage does not interrupt filtration as long as the network continues to provide water at sufficient pressure. Be careful, however: a power outage and a water outage are two different things. If the network supply stops, a system working by its pressure can no longer circulate water.

Finally, domestic filtration remains complementary to official health monitoring. If an authority asks not to consume network water, this directive must be respected even if a filter is installed.

To go further in this comparison, our article on switching from bottled water to filtration looks at the practical differences between these two consumption habits.

What reflexes to adopt in case of a supply problem?

A heatwave does not automatically cause water cuts. But when a drought becomes particularly severe, some territories may encounter supply difficulties.

The first thing to do is to follow local information. A drop in pressure, a scheduled cut, or a health restriction do not necessarily require the same precautions.

If a network interruption is announced, it may be useful to provide a reasonable amount of drinking water corresponding to the household's essential needs for the duration indicated. However, there is no need to create disproportionate stocks if no supply difficulties are announced.

After an incident on the network, also follow the instructions given when the distribution is restored. Depending on the situation, the supplier may ask you to let the water run before use or temporarily apply special recommendations.

In case of a health restriction, do not rely on the clarity of the water or its smell to decide that it can be consumed. Use the water or the alternative solution indicated by the authorities until the measure is officially lifted.

Frequently Asked Questions

Can you drink tap water during a heatwave?
Yes, as long as no local health directive states otherwise. Outside temperature alone does not make network water unfit for consumption.

Should you drink more water when it is very hot?
The Ministry of Health recommends drinking regularly without waiting to be thirsty during high heat. Needs vary, however, depending on age, activity, and state of health.

How do I find out about water restrictions in my municipality?
The official VigiEau service allows you to consult the restrictions applicable locally according to your address and your type of use.

Can drought change the quality of drinking water?
It can change the characteristics of the resources used to produce drinking water. However, the distributed water remains treated and subject to health monitoring.

Is a domestic filter sufficient in case of a ban on drinking water?
No. An official "do not drink" directive must always be respected until it is lifted, regardless of the filtration system installed at home.

During a heatwave, the two priorities do not conflict: you must drink enough and preserve the resource. Keeping water within reach, monitoring local information, and reducing non-essential uses allows you to get through high heat without sacrificing the essential: the water your body needs.

Sources

• Ministry of Health – Heatwaves and their health effects: https://sante.gouv.fr/sante-et-environnement/risques-climatiques/article/les-vagues-de-chaleur-et-leurs-effets-sur-la-sante
• Ministry of Health – Quality of water intended for human consumption: https://sante.gouv.fr/sante-et-environnement/eaux
• Eaufrance – Preventing and managing drought-related crisis situations: https://www.eaufrance.fr/prevenir-et-gerer-les-situations-de-crise
• Eaufrance – Limiting the impacts related to domestic water use: https://www.eaufrance.fr/limiter-les-impacts-lies-aux-usages-domestiques-de-leau
• VigiEau – Information on water usage restrictions: https://vigieau.gouv.fr
• ANSES – Cyanobacteria and cyanotoxins in freshwater: https://www.anses.fr