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Daily Discharge Calculator
Estimate the daily wastewater discharge for a property - the figure used to size a septic tank or treatment plant.
Estimated daily discharge
900 litres per day
For domestic properties only. For commercial premises or larger developments, refer to British Water's Flows and Loads guidance or contact us for advice. A system rated at this figure or above should be specified.
Before a septic tank or sewage treatment plant can be specified, you need to know how much wastewater the property will produce each day. Our free daily discharge calculator gives you that figure in seconds — enter the number of houses and bedrooms, and you’ll see the estimated daily flow in cubic metres per day.
It’s the same calculation used across the industry to size off-mains drainage systems correctly, and it’s the first number our team checks before recommending a system. Use it to get a quick idea of the capacity you’ll need, then talk to us about installing the right system for your property.
What is daily discharge?
Daily discharge is the volume of wastewater a property sends to its drainage system over a day, measured in cubic metres (m³). Every system — whether a septic tank, a package sewage treatment plant or a cesspool — has to be sized to cope with this volume. Get it right and the system runs cleanly for years; get it wrong and you risk a system that struggles, breaches its consent, or has to be replaced sooner than it should.
How the daily discharge calculation works
The calculation is based on a population figure for the property. Each house counts for two people, and a further person is added for every bedroom, which reflects how a home is likely to be occupied over its lifetime. That population figure is then multiplied by 150 litres — the typical amount of wastewater one person produces in a day — to give the daily discharge.
For larger developments, the figure is adjusted slightly downwards, because the more dwellings there are, the less likely every property is to be at peak use at the same time. The calculator handles all of this automatically, so you simply enter the houses and bedrooms and read off the result.
As a guide, a single four-bedroom home works out at around 0.90 m³ per day. A system rated at that figure or above would be suitable.
How to use your result
The figure you get is the minimum daily capacity your system needs to handle. When choosing a treatment plant or tank, look for one rated at that figure or higher.
It’s often worth allowing a little headroom above the minimum. If there’s any chance of extending the property, converting a loft or adding bedrooms in the future, sizing up now is far cheaper than replacing an undersized system later.
Why getting the size right matters
An undersized system can’t treat wastewater properly, which leads to blockages, odours, premature failure and — importantly — a system that doesn’t meet the rules it’s required to. Since 2020 it has been against the General Binding Rules for a septic tank to discharge directly to a watercourse, and systems must be correctly sized and installed to stay compliant. An oversized system, on the other hand, means paying for capacity you’ll never use.
Sizing sits at the heart of a system that’s legal, efficient and built to last. If you’re unsure, it’s always worth a quick conversation before anything is ordered or installed.
When to speak to an expert
This calculator covers domestic properties. Commercial premises, holiday lets, mixed-use sites and larger developments fall outside its scope and should be assessed against British Water’s Flows and Loads guidance — or, more simply, by giving us a call.
Soil conditions also matter. Before a soakaway or drainage field is designed, a percolation test is needed to confirm the ground can take the discharge. We carry out testing, surveys and full installations across West Yorkshire, so we can take a property from first enquiry through to a finished, compliant system.
Septic tank and treatment plant experts across West Yorkshire
DT Groundworks are specialists in septic tanks, sewage treatment plants and off-mains drainage, working throughout Halifax, Huddersfield, Bradford, Wakefield, York and the wider region — and on larger projects nationwide. Whether you’re building a new home, replacing an ageing system or buying a property with a septic tank that needs checking, our team can survey, specify and install the right solution.
Work out the property's population figure — two per house, plus one per bedroom — and multiply by 150 litres to get the daily discharge in litres, or by 0.15 for the figure in cubic metres. Our calculator does this for you. Choose a system rated at that figure or above.
The industry standard is around 150 litres per person per day. A typical four-bedroom home, counted as six people, produces about 900 litres — or 0.90 m³ — a day.
On bigger sites it's unlikely that every property reaches peak water use at the same moment, so a small reduction is applied to avoid over-sizing. The calculator applies this automatically.
No. Since the 2020 General Binding Rules, septic tanks must not discharge directly to a watercourse. Discharge is to a drainage field or soakaway, or a sewage treatment plant is fitted instead. We can advise on what your property needs.
For commercial, mixed-use or large developments, get in touch. We'll assess the site properly using British Water's Flows and Loads guidance and recommend the right system.
At DT Groundworks, we take pride in delivering exceptional workmanship for every project, whether residential or commercial. Our commitment to quality has earned us many loyal customers who trust us for reliable and professional groundwork services. We specialise in septic tank installations, drainage solutions, soakaways, and general groundworks across Yorkshire and beyond. As Street Work and Highways approved contractors and CPCS-registered professionals, we ensure every job meets the highest industry standards.
DT Groundworks
1 Thorngate
Ten Yards Lane
Thornton
Bradford
England
BD13 3SD