Be a septic sceptic!

Dave Vincent of Kingspan Klargester breaks down everything that self-builders need to know about the ins and outs of off-mains drainage, from legal issues to the variety of options available

Building a home in a quiet rural setting offers the owners many benefits; not least peace, beauty and tranquillity! But this type of location also brings additional responsibilities of ownership, not least understanding the impact your new house will have on the landscape and environment around you.

One of the most important considerations is drainage and wastewater management. The starting point here is to look for ways to connect to a main sewer if you can. This is legislated under 2010 Building Regulations and, if need be, you can use a pump station to facilitate the connection. You should arrange a site visit by a suitably qualified engineer – ideally a British Water accredited engineer – to find out if this is possible.

If a connection to the sewer proves impossible then you will need to manage your wastewater (i.e. water drained from baths, toilets, sinks, laundry etc.) safely and securely within the boundaries of your property, using a private drainage product, such as a septic tank or sewage treatment plant.

For many self-builders, for reasons of cost, this means installing a septic tank – a view that is typically backed up in cases where the installer is not a specialist drainage engineer. However, there are hidden dangers in this approach. A very high proportion of septic tank installations are entirely unsuited to the location they are placed in and, as a result, they pose a risk to public health and can cause local pollution. Off-mains drainage is tightly regulated, typically requiring a permit (known as a “permit to discharge”), so choosing the right solution for you requires professional advice from a drainage engineer.

Ultimately, though, the choices we all make should be rooted in a sense of responsibility and stewardship for the land we are living on. When it comes to off-mains drainage, it’s easy to think “out of sight, out of mind” – septic tanks are, of course, buried underground. But that would be dangerous for a product that deals with polluting waste. What’s also important to emphasise is that taking expert advice will ensure you aren’t on the receiving end of an unpleasant new reality, including overflowing toilets or drains!


Legal responsibility for disposing of wastewater lies with you, the property’s owner. If wastewater from your house becomes the cause of local pollution, both you and your installer are at risk of prosecution under The Public Health Act 1936. The penalties can be a heavy fine and a large clean-up bill.

Clearly, there have been quite a few changes to off-mains legislation in England and Wales in the last 10 years or so. For example, the Environmental Permitting Programme – Second Phase (EPP2) introduced in 2010 in England and Wales tried to make off-mains drainage installation a less bureaucratic process.

Under EPP2, owners of small, domestic sewage tanks or plants could, under certain circumstances, be exempt from requiring a permit to discharge if they comply with various conditions. These include following industry installation guidance, incorporating manufacturers’ operational guidance, the British Standard BS6297 regarding soakaway design, and following the advice given by British Water regarding de-sludging and servicing.

You also need to have a product that has been performance-tested and certificated in line with European Standards (EN12566). Further new and binding rules were released for England in January 2015 but while these are helpful, they are open to interpretation. Our message is simple: while the Government has eased the administrative burden on property owners, this should not be mistaken for permission to act irresponsibly and your personal liability remains unchanged.

You should also be aware that further legal changes brought in at the beginning of this year (2020) now mean that septic tanks can no longer discharge into surface water. The General Binding Rules state that if you own a septic tank that releases effluent directly into a ditch, stream, canal, river, surface water, or drain, then you either need to connect to the mains sewer, replace the tank with a sewage treatment plant, or create a drainage field that meets the current British Standard BS6297 2007.


Sewage treatment systems that deal with wastewater vary hugely in terms of how they work and their efficacy i.e. how effectively they can break down solids.


The one product that works extremely effectively, wherever you live, is a sewage treatment plant (STP). A STP is an underground tank which provides an environment where aerobic bacteria can break down sewage and it is highly efficient, treating more than 90 per cent of the pollutants in wastewater.

Packaged sewage treatment systems that have tertiary treatment such as packaged reed beds are the current ‘gold standard,’ bringing the efficiency rating up to 98 per cent. These produce a clear, odourless overflow that is environmentally friendly and suitable for discharging even on sensitive sites, including into a watercourse (subject to Environment Agency/Environmental Protection Agency approval).

Contrary to popular belief, STPs don’t cost significantly more than septic tanks, if you compare both products in terms of installation and maintenance.


A septic tank, by contrast, does not treat waste. It produces soluble waste from solids, and this is then discharged and filtered through the ground. This wastewater is not benign – it contains harmful bacteria. Indeed, under H2 Building Regulations, septic tank discharges are considered harmful and require a tertiary treatment option, such as a reed bed, wherever a tank is installed.

Septic tanks can offer a serviceable solution for some homes, but they need both the right ground conditions, plus a reed bed, to work effectively.

If a septic tank is installed in the wrong location then it can pollute groundwater as well as streams, ponds and rivers. Moreover, if the ground conditions don’t allow efficient filtration (for example, if your house is built on clay soil or on an area subject to flooding) then the soluble waste effluent that the septic emits will collect near the surface, and sooner or later you will know about it.

Testing the ground for its suitability to become a drainage field is usually done by a professional drainage engineer using a percolation test – the correct procedure is described in BS 6297:2007. It’s also worth noting that both H2 building regulations and BS 6297 state that the water table must be one metre below the septic tank outlet.

If you are in any doubt as to the suitability of your garden to filter wastewater, then take the prudent course. Protect yourself and your family, by installing a sewage treatment plant.

Dave Vincent is commercial director at Kingspan Klargester