It may seem an unsolvable problem for mankind, but as at other times in history, we must face this challenge as it has been faced since the beginning of mankind: with technology, division of labour and cooperation. And we are at the right time to solve it: through the digitisation of the water cycle. On the other hand, the planet's water resources are not increasing, but are constant; moreover, the available water is becoming increasingly polluted if we do not take the necessary measures to prevent it. There are 1.4 billion cubic kilometres of water on Earth. Only 0.2 billion cubic kilometres represent the fresh water available for our consumption.

Water is the most important resource

Water, increasingly regarded as a universal common good, is, along with air, the basis of life. It is therefore not enough to say that it is a natural resource indispensable for survival and health, for food production and economic activities of all kinds, as well as for the well-being of individuals and societies. Water is therefore, a priori, a human right that must be satisfied irrespective of any consideration, including financial ones. In 2002, the United Nations Committee on Economic, Social and Cultural Rights (CESCR)The World Water Forum, doubly forced by the physical scarcity of water and the rising costs of its availability, affirmed that access to a sufficient quantity of safe water for personal and domestic uses is a universal fundamental human right. Therefore, ensuring access to water, with all possible technical advances, is a social responsibility that engineers and managers cannot ignore, through the appropriate management of this resource, making use of all available resources.

Where to act to maximise the hydrological resource

Three aspects of the hydrological cycle can be addressed to ensure security of supply, making it more accessible and affordable to the population:

• Increase the availability of water resources.
• Avoid contamination of existing sources.
• Improve the performance of collection, treatment and distribution infrastructures.

On our planet Earth, the absolute amount of freshwater remains roughly constant, but climate change is altering its distribution, making it more extreme and irregular. We have a similar amount of precipitation, but it is distributed unevenly and is more intense for less time, making it harder to collect and store efficiently, leading to run-off, mixing with unwanted elements and thus contamination. Unfortunately, it is no longer possible, except in very specific cases, to increase the availability of the water resource.

In the 60s to 90s of the last century, a great effort was made in this sense, with the construction of around 800 new large dams in Spain. In total, these provide a capacity of some 56,000 hm3 , compared to the 99,000 hm3/year average contribution received by the rivers and the nearly 30,000 hm3/year necessary to meet all demands3 (67% for crop irrigation)4 5. We are the fifth country in the world after China, the United States, India and Japan in terms of the number of reservoirs. However, this does not prevent us from suffering from water stress, i.e. when more freshwater is used than is available at certain periods or its use is temporarily restricted.

As there are hardly any locations left for new reservoirs, it is only possible to expand the water resource through:

• Groundwater exploitation: increasingly scarce and at risk of subsidence if aquifers are overexploited.
• Creation of new desalinated water plants: very costly to obtain both in terms of initial investment and the energy cost of production, and whose waste products can be highly polluting and their disposal harmful to the marine environment.

Global water stress, in % of water consumed in a period of scarcity

Map of potential global subsidence from groundwater abstraction

Both processes are already at the limit of their working range, so we cannot count on much growth unless sophisticated systems are applied to fine-tune their operation by collecting and analysing their operating parameters.

Preventing pollution of freshwater sources

If we manage to at least keep existing freshwater bodies clean or even improve the quality of already polluted water, we will be saving a lot in subsequent treatment. It is difficult to quantify the influence of an uncontrolled discharge in a surface watercourse, but the ratio is close to 1:100, i.e. one m3 of polluted water is capable of polluting around 100 m3 of clean water. To avoid this pernicious effect, it is necessary to work on prevention, using the following strategies:

• Treat the basin holistically, as everything that happens on the surface of the basin affects the basin globally, especially downstream.
• Include rainfall retention and infiltration systems in the upper part of the basin, through the implementation of sustainable drainage systems. That is, surface, permeable, sometimes vegetated elements, part of the urban-hydrological-landscape structure and prior to the drainage system, designed to filter, retain, transport, accumulate, reuse and infiltrate rainwater into the ground, in such a way that they do not degrade and even restore the quality of the water they manage.
• Improve the maintenance of drainage systems, so as to ensure their optimal functioning, avoiding breakdowns and unnecessary expenditure of economic resources.
• Inclusion of purification and filtering systems for water from run-off from major roadways, which have a much greater impact than is generally realised.
• Carrying out public awareness campaigns to avoid using sanitation and rivers as dumping grounds.
• Inclusion of storm tanks to store polluted rainwater, preventing its discharge into the natural environment.

Acting on the performance of existing infrastructures

The efficiency of a process is measured as the quantity obtained divided by the theoretical maximum quantity. In the middle of the 20th century, work was done mainly on improving the mechanical efficiency of water collection, treatment and distribution systems, which are already highly optimised in the industrial process. This has led to a reduction in per capita consumption, but there is still room for improvement, and if a reduction from 2 to 5% in five factors is achieved, a reduction of 15% will be achieved. This can make the difference between maintaining a 100% guarantee of supply or applying periodic cuts. Some of these aspects are:

• In the catchment: Obtaining the optimum mixture from various sources in order to maintain a given chemical composition, pumping rate or treatment.
• In treatment: Review of the chlorine dosage, taking into account the residence time in the distribution network.
• In the distribution network: Reduction of leaks and non-revenue water, optimisation of speeds and pressures in the network, adequate sectorisation, operation in the event of breakdowns and programmed outages, quantification of losses in the event of leaks and controlled emptying and subsequent filling, time for re-pressurisation of the network with consumption, in the case of work by tandeos, optimisation and rationalisation of pumping and tank operation, use of load losses to provide micro-electricity use and reduction of the carbon footprint (or of the energy consumed).
• On water quality: Characterisation of the processes of biofilm formation and removal by changing velocities, optimisation of cleaning campaigns and aeration of the network.
• In household consumption: Remote meter reading, correlation of demand with external variables such as temperature, special dates, holiday periods or pandemics, tests to adjust demand variation with pressure variation, extrapolation of consumption trends and application to public awareness campaigns to reduce consumption.

Once we have defined the problem and the possible levers for action, we will have to use technology to solve it, now and forever.