Your shower water has a second life (and you should take advantage of it)
In Spain we consume an average of 133 litres of potable water per person per day. Of those 133 litres, approximately 45-50 are used in the shower and sink. Water that goes straight down the drain, relatively clean, mixed with a bit of soap and some dead skin. It’s not dirty water — it’s greywater. And discarding it as-is is a tremendous waste.
Meanwhile, in that same household, the toilet consumes another 30-40 litres daily of potable water. Perfectly treated, chlorinated water fit for drinking… to flush waste down a pipe. Quite the contradiction, isn’t it?
Greywater recycling systems solve this paradox: they collect water from the shower and sink, filter it, disinfect it and reuse it to feed the toilet cistern (and optionally the washing machine or garden irrigation). The savings: 30-40% of the household’s total water consumption.
In Valencia, where water stress is not an abstraction but a reality we live through every summer, this goes from being a sustainable option to a strategic decision. Let’s break it all down: how it works, how much it costs, what the law says and whether the numbers add up.
Greywater vs blackwater: the key distinction
First, let’s clarify concepts because confusion is common:
Greywater: Water from showers, bathtubs, sinks and washing machines. It contains soap, skin residue, some body oil and detergent. It’s dirty, but not contaminated in the sanitary sense. With simple treatment, it’s perfectly reusable for non-potable purposes.
Blackwater: Water from the toilet and, in some cases, the kitchen sink (due to food scraps and grease). It contains faecal matter and pathogens. It requires full treatment-plant processing. It cannot be reused with simple domestic systems.
The simple rule: what comes out of the shower and sink is grey. What comes out of the toilet is black. Don’t mix them — that’s key.
How a greywater recycling system works
General diagram
- Collection: Shower and sink drains are diverted to a collection tank (separate from the toilet’s general drain)
- Pre-treatment: Coarse solids filter (hair, threads) — typically a 1-2 mm mesh filter
- Main treatment: Depending on system type (see below), can be filtration, biological treatment or UV disinfection
- Storage: Treated water tank with 100-300 litre capacity
- Distribution: Pump that sends treated water to the toilet cistern (and optionally to the washing machine or irrigation)
- Overflow: When the tank is full, excess diverts to the general drain
- Backup: If the tank is empty (e.g., after holidays), an automatic valve feeds the cistern with mains water
System types
Gravity system (the simplest)
Greywater falls by gravity to a tank located below the drain level (basement, garage, utility space). It’s filtered with mesh filter + activated carbon filter. Stored and pumped to the toilet.
- Advantage: No complex electronics, low energy consumption
- Disadvantage: Requires the tank to be below the collection points. In a Valencia apartment, complicated
- Cost: €1,500-3,000 installed
- Best for: Detached houses with basement
System with pump and mechanical filtration
Collects greywater with a pump, passes it through multi-layer filtration (sand, activated carbon, membrane) and stores it. The pump also handles distribution.
- Advantage: Works in any configuration, including apartments
- Disadvantage: Requires permanent electricity, some pump noise
- Cost: €2,500-5,000 installed
- Best for: Apartments and houses without basement
Biological system (biomembrane)
Uses aerobic bacteria to break down organic matter in the greywater. Then filters with membrane and optionally disinfects with UV. The most thorough treatment.
- Advantage: Higher quality treated water, suitable even for garden irrigation
- Disadvantage: More maintenance, higher initial cost, requires space
- Cost: €4,000-8,000 installed
- Best for: Detached houses with gardens combining sanitary reuse + irrigation
Compact all-in-one system
The most recent. They integrate collection, filtration, UV disinfection and tank in a unit the size of a water heater. Designed specifically for urban apartments.
- Advantage: Compact (80 x 50 x 30 cm), easy to install
- Disadvantage: Limited capacity (50-100 litres), not suitable for large families
- Cost: €2,000-4,000 installed
- Best for: 1-3 person apartments
How much water is saved: the numbers
Let’s do the maths — that’s what we love at Bathscape.
Starting data (family of 3, apartment in Valencia):
- Shower consumption: 40 litres/person/day x 3 = 120 litres/day
- Sink consumption: 15 litres/person/day x 3 = 45 litres/day
- Total greywater generated: 165 litres/day
- Cistern consumption: 6 litres/flush x 5 flushes/person x 3 = 90 litres/day
- Reusable water for cistern: 90 litres/day (from the 165 available)
| Item | Without recycling | With recycling | Savings |
|---|---|---|---|
| Potable water for cistern/day | 90 litres | 0 litres | 90 litres |
| Total potable water/day | 400 litres | 310 litres | 90 litres |
| Daily savings | — | — | 22.5% |
| Annual savings | — | — | 32,850 litres |
| Bill savings (at €3.10/m³) | — | — | €101.80/year |
If you also reuse greywater for the washing machine (another ~50 litres/day), savings rise to 35-40%.
32,850 litres per year per family. That’s 33 full bathtubs. Or, to put it in Valencian perspective, it’s the water that 6 mature orange trees need during an entire summer.
ROI: when does it pay for itself?
Let’s be honest: the pure economic return on greywater recycling is slow. But it exists. And there are factors beyond the water bill.
Compact all-in-one system (€3,000 installed):
| Year | Cumulative savings | Maintenance | Net balance |
|---|---|---|---|
| 1 | €102 | -€50 | -€2,948 |
| 3 | €306 | -€150 | -€2,844 |
| 5 | €510 | -€250 | -€2,740 |
| 10 | €1,018 | -€500 | -€2,482 |
| 15 | €1,527 | -€750 | -€2,223 |
| 20 | €2,036 | -€1,000 | -€1,964 |
With current water tariffs in Valencia (€3.10/m³), the system doesn’t pay for itself within its useful life based on bill savings alone. We need to be transparent about this.
But — and it’s a big but — water tariffs are going to rise. The EU Water Framework Directive requires Spain to apply the cost recovery principle. According to the Spanish Water Supply and Sanitation Association (AEAS), tariffs should increase by 30-50% over the coming decade to cover real costs. With tariffs of €4.50-5.00/m³, payback drops to 12-15 years.
And there’s a factor that doesn’t appear in the table: added property value. A greywater recycling system is a differentiating selling point that property valuers are beginning to recognise, especially in water-stressed areas like the Valencian Community.
In our options comparator you can simulate different savings scenarios for your renovation.
Regulations in Spain: what the law says
Royal Decree 1620/2007
The reference standard for water reuse in Spain is RD 1620/2007. It defines quality criteria for reclaimed water and its permitted uses.
However — and this is important — this standard focuses on reuse at municipal and industrial scale. For in-situ domestic reuse (within your own home), the regulations are more relaxed because there’s no public distribution involved.
Technical Building Code (CTE)
CTE DB-HS4 (Water Supply) establishes that non-potable water networks must be clearly differentiated from potable ones (different coloured pipes, signage). This applies to the recycled greywater circuit.
CTE DB-HS5 (Water Drainage) defines how greywater and blackwater networks must be separated.
Valencian regional regulations
The Valencian Government, through EPSAR (Public Entity for Wastewater Treatment), promotes reuse but has no specific regulations for individual domestic systems. In practice, if your installation is internal to the dwelling and doesn’t discharge untreated water to the sewer, no additional permits are required.
Practical requirements
- Network separation: Recycled greywater pipes must be a different colour (grey or green) and labelled “non-potable water”
- Anti-return protection: Check valve to prevent recycled water from contaminating the potable water supply
- Overflow: The system must have an outlet to the general drain when the tank is full
- Maintenance: Record of periodic maintenance (recommended, not mandatory for domestic use)
Installation: new build vs renovation
In new builds
The best situation. The plumber separates the drain networks from the start: shower and sink drains go to an independent collector that feeds the recycling system. Additional cost versus conventional plumbing: €500-800 in labour + the system.
In full bathroom renovation
Feasible, but with nuances. During a full renovation, cladding is removed and pipes are accessed. It’s the moment to separate drains. What adds complexity:
- You need space for the tank: A utility cupboard, under-counter void or space in the services area
- Diverting shower and sink drainage: Requires additional plumbing work
- Electrical point for the pump: If none exists, one must be installed
- Additional cost in a renovation: €800-1,500 on top of the system price
In a bathroom renovation of an old apartment in Valencia, where pipes are usually lead or cast iron and already need replacing, taking the opportunity to separate greywater networks is a smart decision. The marginal extra cost is small compared to the future benefit.
In a home without works
Complicated. Without access to pipes, separating drain networks is unfeasible without construction work. Systems exist that connect to the shower siphon and store water in a drum, but they’re makeshift solutions we don’t recommend.
Brands available in Spain
Aqus Systems (by Sloan)
Compact under-sink system that recycles sink water directly to the toilet.
- Capacity: 22 litres
- Cost: €800-1,200
- Ideal for: Minimal solution, one sink → one toilet
- Limitation: Doesn’t collect shower water
Hydraloop
Award-winning compact Dutch system:
- Capacity: 100-300 litres depending on model
- Cost: €3,500-5,500 (without installation)
- Treatment: Filtration + UV disinfection + aeration
- Connectivity: Mobile app with real-time monitoring
- Ideal for: Detached houses and large apartments
- Website: hydraloop.com
Pontos AquaCycle (by Hansgrohe)
From the German plumbing giant:
- Capacity: 200-600 litres
- Cost: €4,000-7,000
- Treatment: Biological + UV
- Ideal for: Detached houses
- Strength: Established brand backing, technical service in Spain
GRAF
German manufacturer specialising in water management:
- Range: From residential to commercial systems
- Cost: €2,000-6,000 depending on model
- Strength: Wide variety of sizes
- Availability: Through distributors in Spain
Integration with smart monitoring
This is where it gets interesting for those of us who love technology. Modern greywater recycling systems connect to home automation and allow:
- Real-time monitoring: How much water is recycled, how much is saved, treated water quality
- Maintenance alerts: The system warns you when the filter needs changing or when it detects anomalies
- Integration with leak sensors: If you have a leak detection system, the recycler can automatically close collection if contamination is detected
- Data for energy certification: Documented water savings can contribute to improving your energy certificate
At Bathscape, when we plan a bathroom with integrated home automation, greywater recycling is one of the puzzle pieces. It’s not an isolated system: it connects with everything else. Check our smart bathroom guide for the complete picture.
Environmental impact: beyond economic savings
The economic return on greywater recycling is modest at current tariffs, we admit. But the environmental return is compelling:
- 32,850 litres/year saved per family = less pressure on the Turia and Jucar aquifers
- Reduced load on treatment plants: Less greywater in the sewage network = more efficient treatment plants
- Reduced water footprint: Spain is the third most water-stressed country in Europe (EEA data). Every litre counts
- Multiplier effect: If 10% of Valencia households installed greywater recycling, 48 million litres would be saved daily. That’s 48 Olympic swimming pools. Every day
For those of us who live here and have seen reservoirs at 20% capacity, these figures aren’t abstract. They’re urgent.
Frequently asked questions
Does recycled water smell bad?
If the system works correctly, no. UV disinfection and filtration eliminate the bacteria that cause odours. If it starts smelling, it’s a sign that maintenance is needed (saturated filter or spent UV lamp). Systems with biological treatment best control odours.
Is it safe to use recycled greywater in the toilet cistern?
Completely. There’s no contact with mucous membranes or food. The water goes from the cistern to the toilet bowl and from there to the sewer. It’s the perfect use for recycled water.
Can I use aggressive cleaning products in the shower if I have recycling?
In moderation. Filtration systems tolerate normal soaps and shampoos. But products with bleach, ammonia or strong degreasers can damage biological filters and reduce treatment effectiveness. Use biodegradable products whenever possible.
How much space does the system need?
Depends on the model. Compact ones (Aqus type) fit under the sink. Medium ones (Hydraloop type) need a space similar to an 80-litre water heater: about 80 x 50 x 30 cm. Large ones (Pontos type) need a utility room or garage.
Do I need council permission?
For internal domestic installation (without different discharge to the public sewer), generally no. But consult your architect. If the renovation already requires a building permit, the recycling system is included in the project at no additional administrative cost.
What happens if I’m away from home for a week?
Good systems have a “standby” mode that recirculates stored water so it doesn’t stagnate. If you’re away for more than 2 weeks, some manufacturers recommend draining the tank before you leave. On return, the backup valve feeds the cistern with mains water until the tank fills up again.
Is it compatible with a septic tank?
Yes, and in fact it’s especially beneficial. Less water entering the septic tank = fewer emptying needed = lower maintenance costs. For rural properties in the Valencian Community with septic tanks, greywater recycling has a double benefit.
Conclusion: an investment that looks to the future
As of today, greywater recycling in the bathroom is more of an ecological decision than an economic one. The numbers don’t work out for a 5-year payback at current water tariffs. That’s a fact and we’re not going to sugar-coat it.
But tariffs are going to rise. Water stress is going to worsen. And regulations are going to tighten water efficiency requirements in buildings. Those who install these systems today will be prepared; those who don’t will have to do it later — at greater cost and with more urgency.
Our advice: if you’re doing a full bathroom renovation, at least install the drain separation (grey and black). The extra cost is €500-800 and it leaves you ready to install the recycling system whenever you want, without having to open up walls again. It’s like installing the fibre-optic conduit when your building was renovated in the 90s: those who did it connected to the internet in 10 minutes. Those who didn’t had to break through walls again.
Check our bathroom configurator to explore efficient installation options, or use the BathBuilder to design your sustainable bathroom step by step. We love when technology solves real problems — and water is, without doubt, the most real problem we have in this land.