Sustainable approaches to waste water aren’t just for self-build eco-homes lived in by people determined to lighten their impact on our planet – they can also be a means of helping to achieve Planning Permission and Building Regulations compliance in standard dwellings. Admittedly, the former of these is less significant – it’s likely to be relevant only where the Local Plan requires enhanced water efficiency in order to manage water demand locally and help deliver new homes to local communities. So we’ll start with the more pressing consideration: how waste water can be more sustainable in terms of energy.

More sustainable waste water through heat recovery

Waste water heat recovery (WWHR) is listed by SAP as an energy-saving technology, which means that it can be used to help meet the requirements of Building Regulations Part L. It’s also considered by some to be one of the more cost-effective options when it comes to improving a SAP score, when compared to other solutions such as solar thermal panels, heat pumps, mechanical ventilation and heat recovery (MVHR) or photovoltaic panels (solar electric).

How does waste water heat recovery work? It’s pretty much as simple as it sounds. The system recovers the heat that would normally be lost down the drain when the shower is running, and recycles it. The WWHR device is attached to the shower drain, and uses the recovered heat to pre-heat the fresh cold mains water coming into the property. The best news is the unit takes up very little space, so is easy to incorporate into a bathroom’s design, and there’s no specialist installation required (the WWHR device can be fitted by any qualified plumber). 

Aside from the positive impact of WWHR on a building’s SAP score – and so support of Building Regulations Part L compliance – there are occupier benefits, too. Vertical units (for houses; apartments require horizontal versions) are generally designed to last the lifetime of the building and require no maintenance, plus they’re always running, which means there’s no need for the tenant or homeowner to have to get to grips with a control panel of any kind. It’s said that WWHR can save occupants around 450-500 kWh per person per year, which equates to about £20 each

Secondly, I want to outline the way in which a more sustainable approach to waste water use can be achieved through the recycling of grey water.

More sustainable waste water through grey water recycling

Grey water is the waste water that is discharged from baths, basins, showers and washing machines, and it would normally go into the sewer system via a property’s drains. However, it is possible to take a more sustainable approach to waste water by specifying a grey water recycling system. 

Grey water is classified in the same way as harvested rainwater, so it can only be used for ‘non-wholesome outlets’ such as flushing toilets, washing the car, or watering the garden (though it should not be used for watering seedlings, young plants, or edible crops that are eaten without washing). It’s not permitted to be used for drinking water, bathing, food preparation or dishwashing.

The most common type of grey water recycling system is where waste water from baths and showers is collected, filtered, disinfected, and then used for toilet flushing – this can reduce a household’s water use by 50% (as such, if the property is on a water meter, the water usage bill will be cut roughly in half).

Grey water recycling is considered a more cost-efficient option than rainwater harvesting; the supply roughly meets demand, and there’s no reliance on rainfall, plus the storage tank required will be smaller, saving both space and money. Although we’re mostly talking about domestic dwellings in this blog, it’s worth noting that grey water recycling can offer cost-effective BREEAM points and the Enhanced Capital Allowances scheme is applicable, if you’re installing grey water recycling in a commercial building.

To find out more about how we can help with energy and waste water strategies for sustainable buildings, please call us on 01206 266755 or email