Circular Economy on Beaches: Saltwater Showers

Therefore, the volume of water required per day is

Taking into account the summer period, the total volume of water used amounts to 540 m³.

And considering an average value of 2 €/m³ in Spain, approximately 1100 € would be spent on water per summer period per shower installed.

The design of a shower that works with saltwater must prioritise efficiency, durability and environmental sustainability. The collection system must be simple and have a minimal impact on the environment. It is recommended to use a vertical intake buried under the sand [7], which allows access to the marine water table and takes advantage of the natural filtration of the substrate. This type of collection acts as a natural pre-filter, reducing the presence of particles and sediments in the water before it is pumped to the shower. The latter, vertical drainage, would be the simplest due to the simplicity of the civil engineering work required to collect the water. The complexity of the other types of collection is excessive, as the device to be used should have a manual pumping system that does not require a large flow rate. The pumping system can be based on a manually operated pump or a small, low-power mechanical device. Piston or diaphragm pumps are suitable, as they generate the necessary pressure without relying on electrical power. In addition, their mechanical simplicity facilitates maintenance and reduces the possibility of breakdowns. If an automated system is installed, it is recommended to incorporate non-return valves and a flow regulator to optimise consumption.

The pumped water must undergo a basic filtering and disinfection process. A double filtering system – with a mesh filter to retain coarse solids and a microfiltration cartridge for fine particles – ensures adequate quality for the required use. Disinfection can be carried out using a chlorine dosing device or equivalent solutions, maintaining safe and stable concentrations. This treatment, although mild, is essential to prevent the proliferation of microorganisms in the pipes. All structural and hydraulic components must be made of materials resistant to salt corrosion, such as AISI 316 stainless steel [8], engineering plastics such as high-density polyethylene or PVC-U [9], or glass fibre reinforced composites. These materials offer good durability in coastal environments and require minimal maintenance. In addition, their lightness and strength facilitate assembly, disassembly and recycling at the end of their useful life. The overall design of the installation should allow for quick and safe maintenance. Filters and dispensers should be easily accessible for cleaning or replacement, and the system should include drain valves to facilitate drainage and prevent fouling. A weekly check is recommended during the season of use and a full inspection at the beginning and end of the summer.

Finally, the environmental integration of the system is a key aspect. The shower must blend in with the beach environment, using discreet structures and non-invasive materials. In addition, its operation must minimise energy consumption and avoid any discharge that could alter the marine ecosystem. A well-executed design not only improves the user experience, but also reinforces the commitment to the circular economy and sustainable water management. Subsequently, a search of the literature revealed that since 2007 there has been a registered patent for a prototype that reproduces a system equivalent to the one proposed. Specifically, the ‘Pit Stop’ (patent: November 2007, owned by Armando Clemente Fantini) is also applicable in lakes, rivers, etc. and can be installed on sand or soil [10].

Two commercial alternatives have been found:
a. Ecological Shower - PIT STOP - Refresh Brazil [10].
b. A project for saltwater beach showers (Figure 3) created in Torremolinos seeks to revolutionise bathing in the 21st century [11].

The main indicators of the simplified economic study of the proposal are summarised briefly below:
a. Capital Expenditures (CAPEX): initial estimate ≈ 1000 € per unit (materials, installation and assembly).
b. Operational Expenditures (OPEX): estimated annual maintenance (spare parts, filters, disinfectant) 50 –150 €/year.
c. Annual savings in drinking water: taking into account 540 m³/year and a price of 2 €/m³ → 1080 €/year
d. Amortisation: simple payback ≈ 1–2 years. With a useful life of 10 years, NPV and IRR would be positive in medium water tariff scenarios.

In other words, it has been estimated that the cost of the shower would be amortised in one summer. Assuming that the average lifespan of each shower is around 10 years, the water savings would amount to more than 5,400 m³ and, financially, to 10000 €.

From a social and technological perspective, the adoption of saltwater showers may represent an opportunity to promote environmental education and innovation in coastal infrastructure. Their implementation would serve not only as a water-saving measure, but also as a tangible example of adaptation to climate change and the real-world application of circular economy principles in tourist environments. Technically, the viability of the system depends heavily on critical factors such as the selection of the coastal collection point and a filtration and dosing system calibrated for local water quality. Therefore, it would be interesting to carry out hydrochemical and microbiological sampling at the proposed collection points under different tidal and weather conditions. On the other hand, it would be desirable to build a pilot prototype with instrumentation to measure actual flow rates, frequency of use, disinfectant consumption and water quality parameters (turbidity, coliforms, residual chlorides…).

In terms of economics, it is important to select materials and designs that minimise corrosion and maintenance in a marine environment in order to maximise its life. In addition, it would be appropriate to carry out a life cycle study of the shower and a more detailed economic analysis including maintenance costs in order to obtain a robust sustainability assessment. Similarly, it would be interesting to consider citizen participation and communication campaigns to ensure appropriate use and social acceptance. With these steps, the initiative can be transformed from a proof of concept to a replicable and standardisable solution on coastlines with drinking water shortages. Whatever the case, after completing this simplified study, it can be concluded that it would be very interesting to install saltwater showers on beaches. It is economically profitable from the first year onwards and would involve the responsible use of fresh water.

Society must become aware that anything that does not require high-quality fresh water should be done with reclaimed water, rainwater or, as in this case, salt water, without exacerbating the possible water stress in some regions in the coming years.

The authors would like to thank the Water Hall “CABB” (The Bilbao Bizkaia Water Consortium (CABB, in Spanish), a Business Hall located at the Bilbao School of Engineering, where data to make this revision related to energetic generation along the water supply system of Greater Bilbao were available.

No Conflict of Interest.