Reuse, Recovery & Stormwater
Greywater Recycling Companies
Greywater systems for buildings and campuses, reuse for flushing, irrigation, and cooling make-up.
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Greywater Treatment Train Design: Filtration, Disinfection, and Storage Sizing
Greywater -- wastewater from baths, showers, hand basins, and laundry (excluding kitchen sink and toilet) -- contains BOD5 of 50 to 200 mg per L, suspended solids 50 to 200 mg per L, and coliforms 10 to the 4 to 10 to the 6 CFU per 100 mL. Treatment for toilet flushing and irrigation typically consists of: coarse screen (1 to 3 mm) to remove hair and lint, biological treatment or media filtration (sand or constructed wetland), and UV disinfection (minimum 40 mJ per cm2 per US EPA guidelines). Membrane bioreactor systems achieve effluent quality of BOD below 10 mg per L, turbidity below 1 NTU, and coliforms below 1 CFU per 100 mL for unrestricted non-potable reuse.
System sizing is based on greywater generation rates: 45 to 90 L per person per day for domestic shower and bath greywater. For a 4-person household, expected daily greywater availability is 180 to 360 L. Toilet flushing demand for the same household is typically 50 to 100 L per day (assuming 6 L dual-flush cisterns at 4 to 6 flushes per person per day). Sizing storage at 1 to 2 days' toilet flush demand prevents overflow during low-use periods. Treatment systems are sized for peak flow (morning shower peak, typically 2 to 3 times daily average) and must include a bypass to mains supply during system downtime or excess demand.
Regulatory frameworks vary significantly: UK BS 8525 Parts 1 and 2 cover domestic greywater systems; NSW (Australia) guidelines permit untreated greywater for subsurface garden irrigation only; WHO 2006 Wastewater Reuse Guidelines class treated greywater for urban reuse. Capital cost for domestic systems ranges from $2,000 to $8,000 installed; commercial building systems from $20,000 to $150,000 depending on scale and treatment level. Simple payback is typically 10 to 20 years based on potable water offset at $2 to $5 per kL. Incentives including UK Rainwater and Greywater Management Grants and US EPA WaterSense programme documentation may improve economics.
Frequently Asked Questions
Is greywater safe to use for toilet flushing?
Properly treated greywater meeting BS 8525-1 or equivalent standards is safe for toilet flushing. Treatment must achieve: turbidity below 10 NTU, E. coli below 250 CFU per 100 mL, and BOD below 20 mg per L for indoor non-potable reuse. Untreated greywater must not be used for toilet flushing indoors due to odour from biological degradation within the storage vessel and pathogen risk from aerosol generation during flushing. Systems must include colour-coding of pipework (violet per BS 8525), clear labelling of non-potable supply points, and air gap or RPZ backflow prevention between recycled and mains supplies to prevent cross-contamination of drinking water.
Can I reuse laundry water in a greywater system?
Laundry greywater is higher-strength than shower water: BOD5 100 to 300 mg per L, surfactant content 50 to 150 mg per L, and elevated sodium from detergents (50 to 200 mg per L). High sodium is damaging to soil structure for garden irrigation but acceptable for toilet flushing after treatment. Biological treatment (biofilter or MBR) is required to handle laundry loads before UV disinfection. Avoid using laundry greywater from loads containing bleach or strong disinfectants, which kill biological treatment biomass. Some simple systems (laundry-to-landscape, permissible in California and Australia for subsurface garden irrigation) use untreated laundry water directly to root zones, avoiding treatment requirements but limiting application to below-surface drip only.
What maintenance does a greywater recycling system require?
Domestic greywater systems require: monthly inspection and cleaning of inlet screen and filter media, quarterly check of UV lamp intensity (replace lamp every 12 months or when intensity falls below 30 mJ per cm2 as measured by UV sensor), annual inspection of storage tank for sediment and biofilm (clean with dilute bleach at 50 mg per L free chlorine). Simple biofilter systems require media replacement every 2 to 5 years depending on loading. Electronic control systems (float switches, solenoid valves) should be tested quarterly. Maintain a maintenance log as required by BS 8525 and for insurance/building warranty purposes. Total annual maintenance cost for domestic systems is typically $200 to $500 including UV lamp replacement.
How much water does greywater recycling save?
For a 4-person household, greywater recycling for toilet flushing saves 50 to 100 L per day (20 to 30 percent of total household water consumption of 400 to 500 L per day). Annual savings of 18,000 to 36,000 L are typical. At a potable water tariff of $2 to $5 per kL, this equates to $36 to $180 per year in direct savings. In drought-prone regions (Australia, California, Spain) where water tariffs reach $5 to $12 per kL, payback periods shorten to 8 to 15 years. Larger commercial applications (hotels, offices, sports facilities) achieve faster payback due to higher toilet flush volumes and greater economies of scale in system sizing.
A 250-bedroom hotel in South East England (water-stressed area) was consuming 180 L per guest-night, significantly above the industry benchmark of 120 L per guest-night. Shower greywater from 200 rooms (estimated 30,000 L per day) was being discharged directly to sewer. Thames Water's water efficiency incentive scheme required a 20 percent reduction in consumption as a condition for a new abstraction licence.
Installed a MBR-based greywater recycling system (capacity 35,000 L per day) treating shower and bath water from all 200 rooms. Treatment train: 1 mm inlet screen, biofilter (24 h HRT), MBR (0.04 um hollow fibre membrane), UV disinfection (40 mJ per cm2), and chlorine residual (0.2 mg/L). Recycled water used for WC flushing and laundry pre-rinse. Violet-coded pipework installed throughout. RPZ backflow prevention at every mains backup inlet.
Water consumption fell to 115 L per guest-night (36 percent reduction). Annual potable water saving 9.5 ML per year, valued at 28,500 GBP at local tariff. Thames Water efficiency condition satisfied. System payback 7.2 years on 205,000 GBP installed cost (including pipework alterations). E. coli in recycled water consistently below 1 CFU per 100 mL. No cross-contamination incidents in 3 years of operation.
Questions to Ask Shortlisted Providers
- 1
What treatment train does your system use, and what effluent quality parameters (E. coli, turbidity, BOD, free chlorine residual) do you guarantee for WC flushing application under BS 8525?
BS 8525 Part 2 requires treated greywater for indoor non-potable use to meet minimum quality standards. Different treatment trains (biofilter-UV versus MBR) achieve very different effluent quality. A system that cannot guarantee E. coli below 250 CFU per 100 mL and turbidity below 10 NTU under peak loading is not compliant with BS 8525 for toilet flushing.
- 2
What is the system footprint and energy consumption (kWh per m3 treated), and where will you locate the plant in our building?
MBR greywater systems require space for the tank, reactor, membrane module, UV lamp, and control panel. For a retrofit, confirming that the system fits within available plant room space (typically 2 to 5 m2 for domestic, 10 to 40 m2 for commercial) before design commitment avoids costly building modifications. Energy consumption of 1 to 3 kWh per m3 should be checked against tariff to verify economic viability.
- 3
How does the mains backup (supplementary supply) work when greywater supply is insufficient, and is there an air gap or RPZ valve between the mains supply and the recycled water storage tank?
Greywater systems require mains backup when supply is insufficient (e.g., during low occupancy). The connection between the mains supply and the non-potable distribution must have a compliant backflow prevention device per WRAS Water Regulations 1999 Regulation 25. RPZ valves (BA-rated) or air gaps (Type AA) are required: direct connections are prohibited and constitute a criminal offence under Regulation 25.
- 4
What maintenance does the system require, and do you offer a service contract with defined UV lamp replacement schedule and membrane cleaning programme?
Greywater recycling systems fail silently: UV lamp degradation, membrane fouling, and biofilter drying are not obvious to building facilities teams. A service contract with defined maintenance intervals (monthly, quarterly, annual) and UV lamp replacement schedule (typically every 12 months) is required to maintain BS 8525 compliance. Without it, the system typically degrades to non-compliant quality within 12 to 18 months.
- 5
How is the recycled water storage tank designed to prevent Legionella proliferation, and does the system design address HSE ACOP L8 requirements for non-potable stored water in a commercial building?
Greywater storage tanks in commercial buildings at temperatures of 20 to 45 degrees C are a Legionella risk under ACOP L8. The system must prevent stagnation (water age below 24 hours in the storage tank), maintain a chlorine residual (minimum 0.2 mg/L free chlorine), and be included in the building's Legionella risk assessment and control programme.
What Drives Cost in This Category
Simple biofilter-UV systems cost 2,000 to 8,000 GBP for domestic scale, 20,000 to 80,000 GBP for commercial scale. MBR systems (higher effluent quality, better compliance reliability) cost 30 to 80 percent more. For applications requiring BS 8525-compliant quality consistently (commercial buildings, hotels), MBR's superior membrane rejection of pathogens justifies the premium over simple biofilter systems.
Installing a separate violet-coded non-potable pipework distribution system throughout an existing building is often the largest single cost element: 30,000 to 150,000 GBP for a 250-bedroom hotel depending on building configuration. In new-build, separate pipework adds 5 to 15 GBP per m2 of floor area. Retrofitting greywater recycling to existing buildings without separate pipework is not possible for internal WC flushing.
Payback depends on the volume of greywater available (limited by shower and bath use), the competing use (WC flushing demand), and the local potable water tariff. In water-stressed South East England (Thames Water tariff approximately 3 GBP per m3), a system saving 10 ML per year generates 30,000 GBP annual saving. At a lower tariff (1.50 GBP per m3), the same saving generates 15,000 GBP: the payback period doubles.
RPZ valves cost 400 to 1,200 GBP per unit, with annual test required (typically 200 to 400 GBP per test). Legionella risk assessment update to include the greywater system costs 1,500 to 4,000 GBP for a commercial building. Failure to install compliant backflow prevention or update the Legionella risk assessment creates criminal liability under WRAS Regulations 1999 and COSHH Regulations 2002 respectively.
Key Regulations & Standards
BS 8525 Part 1 (Code of Practice) and Part 2 (Domestic Greywater Treatment Equipment, Performance Requirements and Test Methods) are the UK standards for greywater recycling system design and product performance. Part 2 specifies minimum treated water quality for toilet flushing and urinal supply: turbidity below 10 NTU, E. coli below 250 CFU per 100 mL, and BOD below 20 mg/L. Systems must be designed to achieve these parameters at maximum design flow and under seasonal temperature variation.
Regulation 25 of the Water Supply (Water Fittings) Regulations 1999 prohibits cross-connection between non-potable water systems (including greywater) and the wholesome water supply. An approved backflow prevention device (minimum Type BA Reduced Pressure Zone valve for commercial premises per Water Regulations Guide Category 5) must be installed on any mains water backup supply to a greywater system. Failure to comply is a criminal offence with a fine of up to 1,000 GBP per installation.
Greywater storage and distribution systems in commercial buildings must be included in the building's Legionella risk assessment under HSE ACOP L8 (Legionnaires' Disease: The Control of Legionella Bacteria in Water Systems). Control measures must prevent Legionella proliferation in stored greywater (temperature below 20 degrees C or above 50 degrees C, or biocide residual minimum 0.2 mg/L free chlorine, water age below 24 hours). The duty holder (building owner or responsible person) must maintain a Legionella control scheme and site logbook.
Building Regulations Approved Document G3 sets maximum water use targets for new dwellings (125 L per person per day, optionally 110 L per person per day for enhanced efficiency). Greywater recycling systems contribute to meeting Part G3 targets and are included in the SAP water efficiency calculation (SBEM for non-domestic). Part G also requires non-potable outlets to be clearly labelled 'Not drinking water' and pipework to be distinguished from potable supplies (violet colour coding per BS 8525).