Guide
Executive Summary
Barcelona 2026 Greywater Ordinance
Without a plan for a greywater recycling system in your basic project submittal, your building license will not advance.
Spain’s new water reuse regulation
Real decreto 1085/2024
DBO (Design-Build-Operate): a single party designs, installs and operates the plant under performance obligations (uptime, quality at point of compliance). DBO contracts typically decrease CAPEX but increase OPEX costs compared to self-managed ownership and O&M.
WaaS (Water-as-a-Service) contracts reduce both CAPEX and OPEX from day one: Caskade finances and runs the system. You pay a monthly base fee plus a performance-based €/m³ tariff – typically below your current water spendings – with zero upfront CAPEX and performance/QA contractually guaranteed. This aligns with clients' needs, provides a seamless experience, and simplifies operation & compliance.
Scope
Greywater • Buildings • Spain
Spain • Europe • US • MENA
BUILDINGS • Industry • Agriculture
GREYWATER • PROCESS WATER • Drinking Water
Covered
Excluded
These use cases directly reflect EN 16941-2.
Why Now
Compliance • Restrictions • Costs
1 - Compliance
2025
2024
2 - Restrictions & Operations
Climate change makes extreme droughts more likely and more severe
200 L/person/day cap across all uses (homes, hotels, offices, municipal)
Hotel/tourist water capped at 90–115 L per guest/day
Swimming pools banned from filling/refilling with freshwater (very few exemptions)
Green space irrigation banned, except minimal “survival” watering with non-potable sources
On-site reuse reduces dependence on utility water and keeps essential flows during restrictions while stabilising expenditure.
3 - Costs & Economics
Offices with WC-dominant loads can reach savings of up to ~60%.
Heat recovery adds extra savings: ~20–37% of building energy use.
How It Works
ARCHITECTURES THAT PASS REVIEW
In a Nutshell
Greywater (showers, sinks, laundries) is treated on-site and the purified water used for non-potable purposes: toilets, irrigation and cleaning.
in Detail
Capture
Prioritise showers & bathtubs (large share of water footprint in buildings), add washbasins
Incorporating laundries into the building-level recycle scheme leads to significant gains. For even better efficiency & ROI, choose recycling solutions closer to the washing machines & dryers (Caskade offers solutions ↗).
Rainwater capturing is a great way to add available water volumes but may require civil works. Decide per project.
Treatment
Choose technology, for example:
Filtration + disinfection (UV/chlorine) — compact, proven for WC/cleaning.
MBR (membrane bioreactor) — tighter, steadier quality; preferred for variable-load mixed-use.
Design for EN 16941-2
Building: label greywater and blackwater networks
Connectors: greywater (rainwater) buffer tank with gravity overflow, freshwater input with air gap to prevent backflow, output with overflow (and often bypass) to safely ensure supply.
Operation: Make sure O&M handbook and logs are close to hand. Caskade's solutions come with remote monitoring based on live IoT data. Our O&M teams get notified in case of deviations allowing them to act before any impact.
Distribution
Use the regenerated water for toilet flushing, irrigation of green spaces (non-edible), and cleaning.The distribution takes place via separate, non-potable piping (labelled) which is the standard for new buildings and major renovations anyways.
Economics
Building-level water recycling makes financial sense in most cases
Savings = current water bills* – (reduced water bills* + recycled water Tariff)
*Water bills = costs for potable water + sewer + canon
OEM figures and studies:
Van de Walle (2023, Urban Water Research): reports up to ~30% potable reduction in households (toilet-only) and up to ~60% in offices where WC is dominant.
OEMs claim ~25–45% reduction in potable water use. E.g. Hydraloop cites 25–45%; INTEWA reports ≈50% in some residential use-cases. (Indication; Do not use for design.)
Smith et al. (2018, IWA/Case studies compendium): multi-residential WC reuse projects delivering ~35–45% potable reduction with automated disinfection and QA. (Grey literature but widely cited.)
Friedler et al. (2011, Water Research): building-scale analyses show 30–50% potable substitution potential for WC reuse given typical occupancy and flush volumes; highlights operational controls as key to realising savings.
Compliance & QA
Building-level water reuse in Spain & Barcelona
Barcelona Greywater Ordinance
(BOPB 18/07/2025)
Barcelona is Spain's first municipality to mandate on-site greywater recycling in buildings.
Residential buldings with 16+ dwellings (new construction/significant renovation) – including multi-residential buildings, student housing, etc.
Non-residential buldings with 595+ m³/y water demand (WCs, irrigation and cleaning) – this includes hotels, resorts, offices, spas, sports facilities, etc.
Enforcement: 19 Jul 2026 (one year after BOPB publication)
Design & operations must align with UNE-EN 16941-2 (EU standard for greywater reutlisation)
Submission rule: the basic project must include the concept and pre-sizing calculations, drawings and technical specs; without it, the licence does not advance.
RD 1085/2024 (Spain’s reuse regulation)
It replaces RD 1620/2007 as the national legal basis governing production, supply and use of regenerated water. Design, commissioning and operations must comply with this new, risk-based approach which requires amongst other things:
A risk plan (Plan de Gestión del Riesgo del Agua Regenerada, PGRAR),
defined points of measurement for compliance,
referenced methods/quality classes and,
in practice, ISO 17025-certified labs for quality assurance.
What to do:
Define your point(s) of compliance in your piping & instrumentation plans.
Build a risk plan (PGRAR) covering hazards, barriers, monitoring, corrective actions and roles.
Align sampling to RD 1085 annex methods and keep chain-of-custody.
EN 16941-2:2021 (design & operation)
It’s the base standard for building-level greywater in Europe. Use it to specify sizing, identification/labelling, commissioning (incl. cross-connection tests), O&M, and user information.
ISO 17025 (sampling & lab analysis)
Base standard for lab competence. Ensures sampling, testing, and reporting are valid, traceable, and defensible.
RD 487/2022 (aerosols)
Applies for uses that produce aerosols, for example spray/pressure cleaning. WC cisterns are typically low aerosol risk. RD 1085/2024 requires compliance with this regulation to protect against Legionella.
Playbook
YOUR 7 NEXT DECISIONS & actions – AND HOW CASKADE HELPS
In a Nutshell
Add greywater system to your building planning ASAP
Especially if you are within the scope of the Barcelona Greywater Ordinance, designing late can be costly.
Membrane Bioreactors (MBR) and Ultrafiltration (UF)
These are the two best choices for building-level greywater recycling. Caskade's free review helps determine which one suits your case best. Optionally add heat recovery for additional energy savings. Avoid MBBR and SBR purification.
Water-as-a-service eliminates CAPEX and reduces OPEX
WaaS (Water-as-a-service) provides a fully-managed service at zero upfront investment, reducing OPEX from day one. Alternatively, choose DBO (Design–Build–Operate) or buy the device upfront and mange O&M in-house if you want to be involved more.
Ensure compliance & safety
Both the national RD 1085/2024 regulation (referencing EN 16941-2:2021) as well as the Barcelona Greywater Ordinance require regular sampling & analysis from certified labs. Caskade's Water-as-a-service includes all required compliance and quality measurements and uses remote monitoring based on IoT data for predictive maintenance.
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1) Are you in scope of the Barcelona Greywater Ordinance?
Within Barcelona municipality, and
New building or major renovation, and
Residential buildings: 16+ dwellings (including multi-residential buildings, student housing), or
Non-residential buildings: 595+ m³/y water demand* (including hotels, offices, gyms/sports facilities, student housing, malls/convention venues).
Exempt are hospitals, nursery schools and sites already supplied with municipal regenerated water for those uses.
*Measure annual WC/irrigation/cleaning demand or estimate via occupancy × days × (showers/day × litres/shower + flushes/day × litres/flush) + cleaning/irrigation. Use conservative values, e.g. litres/flush 4.5–6 L, and actual occupancy.
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2) Integrate greywater recycling into your planning ASAP
Things you need to plan for:
Dedicated greywater piping (showers, baths, washbasins)
Plant room footprint and space for recycling device
Non-potable, closed-loop distribution circuit & labelling (EN 16941-2)
Points of sampling & compliance (EN 16941-2)
Caskade packages specifications aligned with EN 16941-2 so architects/MEPs can include them in the basic project definition.
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3) Choose technology
Bioreactor + Ultrafiltration + Disinfection
A membrane bioreactor (MBR) provides advanced treatment. Afterwards, ultrafiltration (UF) and disinfection purify the water to highest standards.
The go-to choice for greywater recycling in buildings, especially when QA stringency is high.
Pros: compact footprint, lower sludge volumes, consistent & low-turbidity effluent, resilient under load swings.
Cons: higher CAPEX; membrane care.
Direct Ultrafiltration + Disinfection
Ultrafiltration membranes (0.01–0.1 µm) remove dissolved particles; UV or chlorine provides microbiological control.
Suitable when the greywater is only lightly contaminated, for example in shower-only or rainwater recycling schemes.
Pros: compact, simple O&M, low CAPEX.
Cons: more sensitive to variable loads; turbidity spikes can reduce effectiveness
Designs to avoid:
MBBR + UF (Moving Bed Biofilm Reactor + Ultrafiltration) • Some engineering firms scale down designs from larger municipal/industrial wastewater plants, but it’s rare in buildings – too many tanks, more complex O&M.
SBR (Sequencing Batch Reactor) + Disinfection • Uncommon in buildings. Takes more operator attention, sequencing tanks don’t fit well in basements, and introduces unreasonable O&M risk in real-world residential settings.
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4) Choose contract model
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5) Prepare documents for building license
Include:
Water recycling concept, specification outline, & pre-sizing calculations,
Layout for risers, plant room, recycling device footprint,
QA plan, and user handbook.
Caskade procures a permit-ready bundle aligned with the Barcelona Greywater Ordinance.
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6) Installation
Installation of MBR / UF devices can usually take place in 1-3 days with minimal disruption thanks to pre-developed modules. The procedure includes a cross-connection test, initial sampling and quality verification (RD 1085/2024), final certification, and the handover including maintenance instructions.
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7) Operation & Verification
RD 1085/2024 requires a documented risk plan (PGRAR) and ongoing operational monitoring. Record keeping is expected and may be audited by the competent authority. The Barcelona ordinance mandates QA sampling and documentation (and availability for inspection).
Quarterly sampling & lab analysis (E. coli at point-of-use; turbidity/SS at outlet; residual/UV logs)
Annual legionella lab analysis if water aerosolising in cleaning
Storage of records & ISO 17025 lab certificates
Volume metering is not explicitly mandated by regulation, but is strongly recommended (and often requested) to evidence performance, support billing/SLAs, and underpin certifications.
Caskade's Water-as-a-service offer includes all mandatory QA measurements and predictive maintenance on its platform for ease of mind.