Key takeaways #
- Grey water recycling under the Green Key certification contributes to an imperative as well as guideline criterion, allowing you to receive and maintain the certification (1, 2 & 3).
- Grey water recycling under the BREEAM certification can contribute up to 6 points in your new-built hospitality project (4).
- Grey water recycling under the LEED certification can contribute up to 10 points in your new-built hospitality project (5).
- Implementation of grey water recycling saves water translating into lower utility bills.
- Higher RevPar (revenue per available room) and ADR (average daily rate) can be achieved with LEED certification (6).
- With the implementation of a sustainable certification, such as LEED, BREEAM or Green Key, you build according to a standard upheld by many financial institutions unlocking green financing (7).
Executive summary #
The hospitality sector, which includes hotels, hostels, resorts, campsites, and other accommodation services, is increasingly adopting sustainable practices to reduce environmental impact. Grey water recycling, which treats and reuses water from showers, baths, washing machines and condensation from airconditioning for non-potable use, is one such practice. This white paper explores how grey water recycling contributes to acquiring and retaining various global certifications and highlights the benefits these certifications bring to the hospitality sector.
Green Key – Grey water recycling creates a solution for the requirements regarding reduction of water for both irrigation and use in swimming pools. Establishments must meet increasing percentages of guideline criteria over the years to maintain certification. Grey water can assist in reaching these goals.
BREEAM – Grey water recycling can contribute up to 6 points in new hospitality projects. Points are awarded based on percentage savings in water consumption compared to baseline levels, influenced by different precipitation zones.
LEED – Grey water recycling can contribute up to 10 points in new hospitality projects. Points are awarded for outdoor water use reduction, indoor water use reduction, and cooling tower water use.
Outlook
The trend towards decentralized water generation, storage, and use is expected to grow, with some regions already implementing regulations for grey water recycling (8). Investment in making buildings “Recycle Ready” will result in financial benefits and higher property values.
Green Key #
The Green Key certification is a leading standard for excellence in the field of environmental responsibility and sustainable operation within the tourism industry. Green Key criteria have been developed for the following categories applicable to grey water recycling: Hotels and Hostels, Campsite & Holiday Park, and Small Accommodation.
To achieve Green Key certification, an establishment must meet criteria related to environmental management, water conservation, waste management, energy efficiency, and community involvement.
Green Key has two types of criteria: Imperative and Guideline. Green key requires you to comply with all imperative criteria. Each year that you want to maintain the green key certification, you must comply with more guideline criteria. Below is an overview of the percentage of guideline criteria you must comply with over the years.
Current Green Key criteria guidelines are applicable from 01-01-2022 – 31-12-2026.
| Year | Percentage of total guideline criteria |
| 1 | 0% |
| 2 | 5% |
| 3 | 10% |
| 4 | 15% |
| 5-9 | 20% |
| 10+ | 50% |
Under criterion 10.3, it is imperative to implement a procedure for conserving water when watering the garden and flowers. This procedure may include using recycled water.
Below an overview of the different guideline criteria that grey water recycling can apply to. For the various categories (Hotels and Hostels, Campsites and Holiday Parks and Small accommodations), the reference numbers may differ.
| Reference number | Short definition | Long definition |
| 4.11 | The swimming pool is covered or has other systems in place to reduce water consumption. | In countries with high temperatures, outdoor swimming pools contribute to a higher environmental footprint through increased water consumption and higher costs due to the considerable amount of water evaporation. Therefore, a swimming pool, when not in use, must have a cover or other system in place (e.g., a gel layer) to prevent evaporation. The cover or other system is to be used outside the operating hours of the swimming pool and/or in periods with no use of the swimming pool. In addition, there could be systems in place to reuse the water of the pool. Due to weather conditions, outdoor swimming pools in certain places and periods of the year use heated water. In this case, use of a cover or other system is strongly encouraged as it also assists in energy saving. During the audit, documentation about the use of a cover or other system for outdoor swimming pools is presented and/or the pool is visually inspected. |
| 4.15 | Wastewater is treated and reused onsite. | To reduce the environmental footprint and to reduce water consumption, the establishment treats its wastewater onsite and reuses it for different purposes, such as fertilizer for fields, in the green areas of the establishment or anywhere else appropriate. The reuse of treated wastewater must be done safely, following national legislation with no adverse effects on the local population and environment. This criterion also includes wastewater derived from the condensation of water in air conditioning systems. During the audit, documentation about the onsite treatment and reuse of the treated wastewater is presented, and the establishment confirms that the use of the treated wastewater does not adversely affect the local population and the environment (e.g., in the form of a confirmation letter on the matter from the competent local authority). |
For more information on the Green Key certification for your region, please consult your local Green Key office.
BREEAM #
BREEAM is one of the world’s leading sustainability assessment methods for master planning projects, infrastructure, and buildings. It recognizes and reflects the value in higher performing assets across the built environment lifecycle, from new construction to in-use and refurbishment. BREEAM offers five levels of rating. Pass, Good, Very Good, Excellent and Outstanding. Note that the benchmark percentages, the categories, and the number of credits per category can differ per country. The reason is the difference in building regulations and climates. The information in this white paper for BREEAM is based on the BREEAM International New Construction Version 6 guidelines.
| BREEAM Rating | % score |
| Outstanding | > 85% |
| Excellent | > 70% |
| Very Good | > 50% |
| Good | > 45% |
| Pass | > 30% |
| Unclassified | < 30% |
Within the water category, there are four different subcategories. WAT 01 Water Consumption, WAT 02 Water monitoring, WAT 03 Water leak detection and prevention, WAT 04 Water efficient equipment. In total, there are 9 credits to be earned in the water category.
Grey water recycling can contribute to 5 credits in the subcategory WAT 01 Water Consumption. The number of credits earned depends on the percentage of savings achieved compared to the baseline level. The different BREEAM precipitation zones influence the required percentage savings for each credit.
| No. of BREEAM credits | Percentage improvement | ||
| Precipitation zone 1 | Precipitation zone 2 | Precipitation zone 3 | |
| 1 | 12.5% | 12.5% | 12.5% |
| 2 | 25% | 25% | 25% |
| 3 | 40% | 35% | 35% |
| 4 | 50% | 45% | 40% |
| 5 | 55% | 55% | 50% |
| Exemplary | 60% | 65% | 60% |
World map of BREEAM precipitation zones
Extra credit can be earned under the Innovation category Inn 01. This can be done in two ways.
Through the application of the Hydraloop grey water recycling system as an innovation in the building. Innovation applications can be submitted to BRE Global by a licensed BREEAM Assessor using the formally approved innovation application form available on the BREEAM website. Note that this credit can only be earned one time per country. It is therefore possible that Hydraloop, as an innovation credit, has already been claimed by a different party and is therefore not available anymore.
When the grey water recycling system can achieve level 5 of WAT 01 Water Consumption and > 95% of WC or urinal flushing demand is met using recycled non-potable water.
Below is an example of how the BREEAM score for a new construction version 6 is calculated. Depending on the scope of the project (Shell only or Shell and Core) and the environmental sections, credits can be awarded and weighted accordingly.
| BREEAM section | Credits achieved | Credits available | Credits achieved, % | Section weighting (fully fitted) | Section score |
| Management | 10 | 20 | 50.00% | 0.12 | 6.00% |
| Health and wellbeing | 17 | 21 | 80.95% | 0.14 | 11.33% |
| Hazards | 1 | 1 | 100.00% | 0.01 | 1.00% |
| Energy | 16 | 32 | 50.00% | 0.19 | 9.50% |
| Transport | 5 | 11 | 45.45% | 0.08 | 3.63% |
| Water | 5 | 9 | 55.56% | 0.06 | 3.33% |
| Materials | 10 | 14 | 71.43% | 0.125 | 8.92% |
| Waste | 3 | 13 | 23.07% | 0.075 | 1.73% |
| Land use and ecology | 5 | 5 | 100.00% | 0.10 | 10.00% |
| Pollution | 9 | 12 | 75.00% | 0.10 | 7.44% |
| Innovation | 2 | 10 | 20.00% | 0.10 | 2.00% |
| Final BREEAM score | 64.88% | ||||
| BREEAM rating | Very Good |
For more information on the specifics of the BREEAM certification for your region, please consult a local BREEAM expert.
LEED #
LEED BD+C Hospitality (building design and construction). LEED certification is a globally recognized symbol of sustainability achievement. It provides a framework for healthy, efficient, and cost-saving green buildings. LEED-certified establishments must adhere to strict guidelines on energy use, water efficiency, and indoor environmental quality.
LEED offers four levels of certification. Certified (40-49 points), Silver (50-59 points), Gold (60-79 points), Platinum (80 points and above). The focus of this paper is on LEED BD+C Hospitality (Building design and construction).
In the category WE Indoor Water Use Reduction, grey water recycling can contribute 1 to 6 points. With a reduction in fixture and fitting water use from the calculated baseline earned.
| Percentage reduction | Points (BD&C) | Points (Schools, Retail, Hospitality, Healthcare) |
| 25% | 1 | 1 |
| 30% | 2 | 2 |
| 35% | 3 | 3 |
| 40% | 4 | 4 |
| 45% | 5 | 5 |
| 50% | 6 | – |
In the category WE (water efficiency) Outdoor water use reduction, grey water recycling can contribute 1 to 2 points, depending on the reduction of the project’s landscape water requirement (LWR). Table 6 shows the points’ requirements.
| Percentage reduction from baseline | Points (except Healthcare) | Points (Healthcare) |
| 50% | 1 | 1 |
| 100% | 2 | – |
In the category WE (water efficiency) cooling tower water use, grey water recycling can contribute 1 to 2 points. With the use of at least 20% recycled non-potable water in the cooling towers.
For further information on the specifics of the LEED certification for your region please consult a local LEED expert.
Benefits of certification #
Achieving one or more of these certifications can significantly benefit your establishment in the following ways.
Improved operational efficiency, with the implementation of grey water recycling, the water savings translate into lower utility bills. Per project, Hydraloop can calculate different financial metrics based on the local water tariff, such as the break-even year, ROI (Return on Investment) and MOIC (Multiple on Invested Capital). Contact Hydraloop for more information.
Higher RevPar and ADR (revenue per available room) and (average daily rate), as research has shown, LEED (v4) BD+C certification increased the ADR for U.S. hotels with $20 after the certification was implemented (6).
Access to green financing, with the implementation of a sustainable certification, such as LEED, BREEAM or Green Key, you build according to a standard upheld by many financial institutions according to which it is determined whether the establishment can qualify for green financing. Green financing offers the loanee the advantage of better loan terms. For example, discounted interest rates (7).
Impact on property value #
Grey water reuse not only drastically reduces the use of precious drinking water and reduces the wastewater flow, but it also increases the value of the building. A recent study by the NVM (The Dutch Cooperative Association of Real Estate Agents and Appraisers) shows that houses that are not energy-efficient are significantly less valuable. With an average of 113 square meters, an A-label house is worth €434,900. – The same house with a G-label is worth €365,700. – The price difference between energy-efficient houses with labels A and G is €69,200. – or 16%.
Peter Fiske, founder and Executive Director of the National Alliance of Water Innovation (NAWI), foresees a water transition, like the one we are seeing with energy, as presented during the 2023 UN water week in New York, USA (8). NAWI has received $110M funding from the U.S. Department of Energy to research how to dramatically lower the cost and energy of desalination and water reuse through a 5-year program of early-stage applied research (9). Traditionally, we generated our energy centrally (per city of municipality) and transported it to individual households. Nowadays, a mix of central and decentral energy use and storage is common. With solar panels and batteries, a large part of the household’s energy use is decentral generated, stored and used.
The expectation is that we will see a similar development with water. A mix of central and decentral generation, storage and use will become common on a global scale and in some places is already common. In Spain, Chili, Florida, and Hawaii there are already regulations in place making it obligatory to prepare a building Recycle Ready or incentivizing grey water recycling. Based on this expectation we can conclude that the investment to make a building Recycle Ready will be financially beneficial. For every type of building, including hotels, holiday parks and campsites, the investment in making the building Recycle Ready will result in a higher property value (10).
Sources #
Green Key criteria and explanatory notes Hotels and Hostels, Green Key, (2022), retrieved from https://static1.squarespace.com/static/55371f97e4b0fce8c1ee4c69/t/657811a969db543110f4cfe1/1702367658219/Green+Key+criteria+and+explanatory+notes+2022-2026+hotels+and+hostels.pdf
Green Key criteria and explanatory notes Campsites and Holiday Parks, Green Key, (2022), retrieved from https://static1.squarespace.com/static/55371f97e4b0fce8c1ee4c69/t/657811f2374e0d141838dc55/1702367732025/Green+Key+criteria+and+explanatory+notes+2022-2026+campsites+and+holiday+parks.pdf
Green Key criteria and explanatory notes Small Accommodations, Green Key, (2022), retrieved from https://static1.squarespace.com/static/55371f97e4b0fce8c1ee4c69/t/6578121bbd75ee62ed7ed2b5/1702367772518/Green+Key+criteria+and+explanatory+notes+2022-2026+small+accommodations.pdf
BREEAM International New Construction Version 6, Tina Stronach (2022), retrieved from https://files.bregroup.com/breeam/technicalmanuals/sd/international-new-construction-version-6/?utm_campaign=2241538_BREEAM%20NEW%20NC%20manual%20downloads&utm_medium=email&utm_source=BRE&dm_i=47CQ,1C1KY,8MU4FN,667EQ,1
LEED Reference Guide for Building Design and Construction, U.S. Green Building Council (2019)
Cornell hospitality report, The impact of LEED certification on hotel performance, Matthew C. Walsman Rohit Verma, Suresh Muthulingam (2014), retrieved from https://ecommons.cornell.edu/server/api/core/bitstreams/4d72b788-0889-455e-9897-917121e9c8a3/content
ESG in hotel real estate: Green financing and what it means, Kimberley Yoong (2022), retrieved from https://hospitalityinsights.ehl.edu/esg-in-hotel-real-estate
Peter Fiske presentation @ UN2023 Water Conference Hydraloop side-event, NAWI (2023), retrieved from https://www.youtube.com/watch?v=7dYHX-Tssqc
Berkeley Lab, Peter Fiske (2024), retrieved from https://profiles.lbl.gov/31851-peter-fiske
Energielabels op de woningmarkt, NVM & Brainbay (2024), retrieved from https://www.nvm.nl/media/w3xm2oy0/bijlage-4-energielabels-op-de-woningmarkt-themaonderzoek-bij-nvm-kwartaalcijfers-2024-1.pdf