Greywater recycling

What is greywater recycling?

'Greywater' refers to all wastewater generated in buildings from streams without fecal contamination – i.e. all streams except for the wastewater from toilets. Greywater recycling, then, refers to the treatment of wastewater from appliances such as showers, baths and sinks, to be re-used and fed back into a property for non-potable purposes such as flushing toilets.

How does a greywater recycling system work?

First, wastewater is collected from appliances and fed into a collection unit (via pumps or gravity). The collection unit removes contaminants using biological, chemical and physical actions.

From here, the wastewater is pumped into a treatment system for 'ultrafiltration' which prevents particles, bacteria and viruses from passing through to the next stage of the system.

The treated water is stored in a tank before being pumped out for re-use in toilet flushing or irrigation on-demand (the greywater cannot sit for extended time periods in the tank otherwise it is at risk of becoming contaminated).

What are the business benefits of greywater recycling?

Greywater recycling is most suited to businesses that need a constant supply of water for use in baths, basins and toilets. In this regard, hotels, large offices, residential blocks and leisure centres will find the system particularly attractive.

Greywater can account for 30-50% of the wastewater that is discharged into sewers. While it is likely that treated greywater will not be safe to drink, recycling it can significantly reduce water bills for businesses.

Greywater recycling has been shown to reduce water consumption by up to 40%. According to Thames Water, London is set to suffer from a shortfall of water of 414 million litres a day by 2040, meaning that the cost of water will rise with demand.

Some greywater recycling systems allow businesses to save on water costs without any changes to staff behavior and actions. For instance, the systems can be fitted with built-in telemetry to transmit system data and live diagnostics, giving businesses greater maintenance over their water systems.

Alongside reductions to water footprints, greywater recycling can reduce carbon emissions and energy use – some low-energy systems are capable of produce a cubic metre of of water using just 1.5kw/h energy.

It should also be noted that greywater recycling systems will compliment other on-site sustainability solutions and can increase credits for companies attempting to secure BREEAM or LEED building standards.

How much does a greywater recycling system cost?

There is no single figure for the installation costs of a rainwater harvesting system – it will fluctuate based on the size of the system and whether it is being retrofitted into existing infrastructure.

Payback on a greywater recycling system generally ranges from 2.5 to five years, based on whether the system is 'on-demand' or 'batch'. A batch system uses a low-pressure filtration method which has lower energy consumption, but more space is required for the tanks. An on-demand system is smaller and takes a high-pressure approach to deliver rapid ultrafiltration. Installation costs are lower, giving a faster return on investment. 

It should also be noted that businesses that install greywater recycling systems are also eligible for the Enhanced Capital Allowance (ECA) initiative to reduce upfront expenditure. ECA allows business to claim a tax relief for the first year of investment. For water recycling projects, ECA covers 100% of the first-year allowance of investments, writing the project off against taxable profits.

What are the key business requirements when intalling a greywater recycling system?

Ideally, greywater recycling systems should be designed as a building specification prior to the construction of the building. Specific pipework and the need for space for the filtration and storage tanks makes retrofitting a costly undertaking.

Installations are usually managed by a dedicated technical account manager from an installer, who will provide site-specific advice to the business once completed. Once in place, greywater recycling systems will require annual inspections and are low-maintenance.

A system with built-in telemetry will gather real-time data for the system, so businesses can be preventive to any issues and manage the system more thoroughly. Some online platforms – such as Waterline – will run reports on the performance of the system. Businesses can used these platforms to verify water savings.

How does greywater recycling differ from other water re-use systems?

Greywater recycling systems utilise the wastewater from internal appliances in a building. This excludes wastewater contaminated through toilet discharges, which can be treated through blackwater systems. Greywater is easier to treat compared to blackwater because no faecal matter can leak harmful pathogens into the water.

Greywater recycling is different to rainwater harvesting, which collects rainwater as an alternative source of water. Greywater recycling systems usually have a quicker return on investment than rainwater recycling systems, and benefit from not depending on weather circumstances. While rainwater harvesting can reduce water consumption by around 30%, it is estimated that greywater recycling systems can deliver up to 40% in water savings. 

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