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Water efficiency in buildings

It is estimated that in Portugal household costs for housing, water, electricity and gas exceed 30% of total monthly and annual household costs, according to INE data from July 2017. In buildings, at national level and in the European Union, there is an estimated potential for water savings of 30% by adopting water efficiency measures. By using more efficient systems, taking advantage of innovative solutions, equipment and technologies compared to conventional systems, savings in buildings can reach 45% of water consumption. In the residential sector, the most representative uses of water are associated with baths and showers (around 39%) and household appliances (around 20%). Saving water also means saving energy, at home and in our community, since the collection, transportation and treatment of water supplies (and wastewater) are operations with high energy consumption and costs that can be reduced through more efficient use of water and energy.

The construction market has been evolving, diversifying solutions and building supply, and should be a partner in advising consumers on measures and investments to adopt. In this article, adapted from the document “Water efficiency in buildings” and prepared by Aqua eXperience, we’ll tell you about the main water efficiency measures and solutions that can be useful when buying sanitary equipment, renovating or building new.


Water efficiency measures to adopt in residential buildings – 5R principle

As with waste, within the 5R principle (reduce consumption, reduce losses and waste, reuse water, recycle water and use alternative sources), reducing waste and consumption is the first essential step in adopting more efficient water management at home. In buildings, special attention should therefore be paid to reducing water use times. Certified products labeled as more water-efficient should be taken into account when choosing them. Identifying water losses in household networks or equipment (e.g. taps, showers and cisterns) is an important step in reducing waste. In addition to these measures, it also makes sense to evaluate and improve the overall efficiency of buildings (in single-family homes or condominiums, for example), considering the reuse or recycling of water (e.g. gray water) and the use of alternative sources (such as rainwater).

One of the ways to reduce water consumption is to choose the right products/devices for using water in buildings, which ensure greater efficiency and equal or better comfort. On the other hand, there should be concern about optimizing the time spent on each use. The choice of household appliances that use water (e.g. dishwashers and washing machines) should also take into account their water consumption.

In addition to the renovation and replacement of devices and equipment, there are domestic hot water circulation and return systems which, as well as being a factor in increasing comfort in use, are also a water efficiency measure.

There may also be water losses (physical losses) caused by deficiencies/breaks in the building network which must be repaired, but which are not called waste because they are not associated with misuse of water by the consumer. However, identifying them is essential for reducing the amount of water that buildings waste. Intelligent water consumption monitoring and management systems help to identify these situations.

There are water-saving systems for buildings that consist of reusing and recycling black water [water that comes from flushing toilets and urinals] and gray water [domestic wastewater that does not contain black water, from uses such as bathing or washing dishes or clothes, among others].

Among these, the use of graywater as an alternative domestic source may be the most viable, since it should require less treatment for the same use. However, the amount of gray water produced can vary considerably depending on the sanitary habits and lifestyle of families. There are also rainwater harvesting systems that can generate significant savings in buildings, particularly in those where there are garden areas or areas for washing floors and cars, in addition to flushing toilets, washing machines and other uses (e.g. cooling towers), but they must be sized and adapted on a case-by-case basis.

In order to ensure their operation during periods when there is no rainfall, these systems must be equipped with an alternative water supply system, so that water can be supplied without interrupting the supply from the non-potable network.

In these cases, it is advisable to install systems that manage and switch supply sources automatically and safely. The impossibility of cross-connections, i.e. allowing this water to enter the drinking water network, must be guaranteed in all situations.

To find out how far water efficiency can go in buildings or homes, it is already possible to request a diagnosis of the current situation. The diagnosis of the current situation helps to identify and subsequently implement direct water-saving measures in the most appropriate places, as well as indirect measures, in terms of behavior, which can immediately improve efficiency of use without the need for interventions in the building.

Real solutions that we can already adopt

So that we can take action and make decisions that are best suited to each situation and each building, here are some real solutions:

In older buildings, the choice of more water-efficient devices can be an opportunity to rehabilitate the building’s network, for example in the event of a lack of flow or pressure in the network, or when deposition phenomena occur in the pipes. In this case, the building network should be renovated using materials certified for drinking water, which are durable and resilient so as to minimize the risk of breakages, and in accordance with Portuguese/European certification standards.

The installation of water consumption management systems, which consist of connecting the building network to remote management systems with information on your own consumption habits, can provide access to the usage profile of each home. In this way, you can learn about your own consumption and adopt daily behavioral measures to use water more efficiently, as well as identifying water losses in networks and equipment, if water is consumed during periods of non-use (e.g. at night). These intelligent systems can be installed in homes or condominiums, whenever there are partial meters and it is possible to request the service from your management entity.

Purchasing more energy and water efficient appliances can generate savings of around 51% in water consumption for washing machines and 41% in consumption for dishwashers. Currently, the most energy-efficient appliances correspond to energy classes from D to A, with the higher class leading to lower water and energy consumption. From a water point of view, the most efficient appliances should be those with the lowest water consumption (liters per year). When choosing this equipment, in addition to energy class C or higher, look for machines whose label indicates an average annual water consumption of less than 10,000 liters per year (washing machines) and 2,500 liters per year (dishwashers).

In cistern systems (which account for some of the highest water consumption in the building cycle), there are more efficient mechanisms and others that support adjusting the flush volume, for example according to use (dual flush or interrupted flush, with the option for the user to stop). Still others give you the possibility of using a lower volume than the original for the same room (by replacing it with more efficient mechanisms), without having to replace the cistern tank you currently have. In all situations, the drainage system should not be compromised, avoiding blockages. In general, efficient cisterns have between 4 and 5 liters of total volume, considering an D rating or higher.

Showers and shower systems can account for a further 30% of average daily household water consumption. The most efficient (D rating or higher) should have water consumption of between 5 liters per minute and 7 liters per minute. In addition to reducing water consumption, showers and shower systems can also reduce energy consumption in proportion to the hot water required. For reasons of efficiency and user comfort, there are also systems that incorporate thermostatic taps (with a stable temperature) or “eco-stop” taps (with a timer to cut off the flow).

The taps that are distributed around the kitchen and bathrooms in your home can account for around 16% of consumption in the residential sector in Portugal. For washbasin taps (homes), the typical model considered, classified with the letter D, is one that has a water consumption of up to 2 liters per minute. For kitchen taps, the typical model considered, classified with the letter D, is the one with a water consumption of up to 4 liters per minute. Taps with a flow rate of less than 4 liters per minute (located at the sink) and a flow rate of less than 2 liters per minute (located at the washbasin) should have an aerator, in order to provide more comfortable use, equivalent to the use obtained with higher flow rate taps.

To minimize water consumption and comfort, without replacing devices, users can also purchase flow reducers to better adjust the volume consumed for each use.

To avoid wasting water from the moment you turn on the tap until you get the water at the desired temperature for domestic hot water, you can install systems or equipment for circulating and returning hot water or water heat recovery equipment. The installation of these systems is generally recommended, where possible, in hot water networks where the distance between the producing appliance and the furthest point of consumption justifies it.

For washing or outdoor spaces, because they represent a high consumption of water, often of a quality that is too high in relation to its use, you can adopt strategies to improve their efficiency, in terms of equipment and the programming of watering periods and adaptation to the weather conditions of the land and crops. Rainwater harvesting and water reuse systems can be other sources of water for watering and washing outdoor spaces. Ideally, an efficient irrigation system should be installed in all gardens and similar areas (e.g. drip systems), and if the area to be watered is extensive, the sprinkler method should be adopted, due to its greater efficiency and ability to adapt to any terrain configuration.

In a swimming pool, solutions that guarantee greater water efficiency act on filling and maintenance, namely by guaranteeing watertightness and reducing leaks and losses through overflow and evaporation. Proper maintenance of the pool’s water quality, through more efficient processes and recirculation, can also prevent the use of unnecessary water. The pool should be cleaned to minimize clogging of the treatment filters and, consequently, the frequency of washing them. The water used to clean the filters can be used for other purposes, such as irrigation, if the water quality aspects of the use are properly checked.

The measures outlined for the exterior can be complemented by covering the landscaped grounds with solutions such as pine bark, rolled stone, gravel or volcanic rock, as they retain moisture in the soil for longer, reduce the germination and development of weeds, promote the stabilization of soil temperature, favouring the proper development of roots and soil organisms, and prevent erosion and compaction caused by heavy rain.

To retain rainwater and guarantee thermal comfort and waterproofing protection, you can opt for green or garden roofs, which consist of installing vegetation on top of a built structure. These systems must be properly sized and require maintenance.

Along with choosing more efficient equipment and devices (with lower water consumption), it is essential to ensure that water use is more appropriate, by reducing the time spent on each use and adopting water-saving strategies, which translate into savings on the bill.


Increasing water efficiency in residential buildings is increasingly within everyone’s reach, benefiting from ongoing technological developments and the continuous development of innovative products and solutions. There are many areas of a building with the potential to reduce waste and water consumption. At Beelt, we want to be part of the solution for a more sustainable world, and we support our customers in making more efficient choices.


Information transcribed and adapted from the document “Water efficiency in buildings – Aqua eXperience Guide”, published in Aqua eXperience, promoted by ADENE and EPAL, and with support from the Environmental Fund and ENEA 2020.


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