Back to Basics: Practicalities of Private Sewage Treatment
South Cumbria Rivers Trust simplifies the complex challenges of private sewage.

22nd January 2025
Over the next few issues of the newsletter, South Cumbria Rivers Trust will provide essential information for owners and operators of private sewage treatment systems, including those not connected to main sewage, and what they can do to minimise the environmental impact.
The world of sewage treatment can be a tricky area to understand. So, let’s start from scratch. The term sewage refers to all the dirty water from your house that needs treating, whether that be from your sink, shower, washing machine, or toilet. Sewage needs treating before it goes out into the environment because we don’t want solid particles and/or dissolved chemicals contained within sewage to end up in our watercourses.
Key pollutants from wastewater that can cause environmental issues include organic matter, nutrients, and pathogens. When organic matter enters rivers or streams, it is quickly broken down by microorganisms and, just like a compost heap, will decompose and use up oxygen from the water through respiration.
In a wastewater context, this is typically called the Biological Oxygen Demand (BOD). Lower amounts of oxygen in the water can harm creatures that depend on dissolved oxygen to survive, leading to reduced biodiversity, amenity value, and overall ecosystem damage.
Why focus on Phosphorus (P)?
In order for plants to grow, there is a specific ratio required for Phosphorus (P) and Nitrogen (N), that varies from species to species. If the P requirement is not met, it doesn’t matter how much N is in the environment, growth will be limited. Hence, why P is classed as a limiting nutrient in aquatic systems. If the limiting nutrient is in excess, it will result in excessive growth. There are far more complex systems taking place but it highlights just how important P is.
As P comes from various sources, such as humans and animals, the Love Windermere Partnership is focussing on reducing P into the lake, including inputs from septic tanks and private sewage treatment plants. The Environment Agency SAGIS Report published in 2023 estimated that these sources contribute 16-24% of the total P load entering Windermere.
Finally, pathogens like bacteria and viruses are also important to remove from wastewater before it is discharged into the environment. That’s because of their potential impacts on health, especially considering Windermere is used for a whole host of recreational activities, including swimming and water sports. (For more information visit Bathing water quality (data.gov.uk))
We hope you found this information helpful and look forward to the next issue, where we will discuss the various types of systems available for private sewage treatment, followed by best practices for their operation and maintenance. In the meantime, head over to the Call of Nature website, if you want to know more: www.callofnature.info
