In the UK, discharges to the environment are regulated by the Environment Agency. These rules cover septic tank discharges into ditches and other areas. The current regulations are set out in the general binding rules and apply to everyone as of this year (2020).
With respect to discharging to a ditch (or stream/river), the general binding rules state that you must apply for a “permit to discharge” if you are:
Technically speaking, the regulations do not say that you cannot discharge to a ditch with a septic tank. However, they do say you will have to apply for a permit since you aren’t using a sewage treatment plant. Given that you also have an obligation not to pollute, it would be extremely unlikely that a permit to discharge septic tank water into a ditch would be approved.
Water from a septic tank is high in ammonia which kills plant life and can pollute the land.
If you are adhering to the criteria laid down in the general binding rules and use a treatment plant you won’t have to make the application for a permit and can avoid the lengthy forms and cost.
We have written a full article on the general binding rules which is useful to read if you want to go through all the criteria for discharges to the environment.
Owls Hall has a number of products and services available that will help you if you’re considering a new sewage system for your home or business, or if you’re concerned about maintaining your current system.