Onsite wastewater systems

For those of us who have lived most of our life in the cities, our hands-on responsibility for the operation of sewage systems has generally been limited to closing the toilet seat cover, periodic cleansing of the toilet bowl, and an occasional application of a plunger. Beyond that it is someone else’s problem. Moving to the country, either on a full or part-time basis, changes all that. Those unknown processes that, in the city, are handled by the local government are now solely our responsibility as individual property owners.

It turns out, that in most cases, taking responsibility for operating your water treatment system is not such a big deal. The processes are relatively straightforward and maintenance of most systems is relatively simple. It just takes a bit of knowledge and a reasonable amount of good old common sense. (See Caring for your Septic System.)

This section will provide some of the information you need to understand the basics of “onsite wastewater systems”, some do’s and don’ts, and references for further information.

What’s the big deal?

Most of us know that what we put into our toilets and down our drains is both unpleasant and potentially dangerous. It contains a variety of disease causing bacteria, viruses, and parasites. It is common sense that it must be kept from contaminating our sources of drinking water and from lakes and rivers used for recreational purposes.

Did you know that domestic wastewater also contains nutrients (nitrogen and phosphorous in particular) that can promote algal blooms and cause premature aging of lakes? Bridge Lake and other lakes in the area already contain large amounts of nitrogen. The addition of even small amounts of phosphorous can combine with the available nitrogen to cause dramatic growth of algae and other vegetation.


How does a system work?     

Onsite wastewater systems are designed to treat domestic wastewater before it reaches groundwater, wells, lakes and rivers. The most common system includes a septic tank and drainage field. In this arrangement, wastewater flows or is pumped from the house to a buried tank, where solids settle to the bottom, oil and grease float to the top and the remaining “water” flows through to the drainage field. The drainage field is an arrangement of perforated pipes buried in the ground. Treatment occurs both in the tank where anaerobic bacteria break down the solid particles, and in the drainage field where organic matter becomes food for microorganisms in the soil and bacteria and viruses are trapped and die off. The treated water migrates both to the surface where it is removed by evaporation and down to the groundwater. Most other residential systems are variations on this basic treatment system.

Construction, Alteration and Repair

Onsite wastewater systems are within provincial jurisdiction and are specifically addressed by the Sewerage System Regulation under the Health Act. Under the regulations all work on new systems, repairs to systems and maintenance of systems constructed after 2005 must be carried out by “Authorized Persons”. These are professional engineers or technologists certified as Registered Onsite Wastewater Practitioners (ROWP) to carry out work (planning, installing, maintaining) on onsite systems. Public Health Inspectors no longer inspect and approve systems. The full responsibility to get it right and to effectively operate the system rests with the property owner and the Authorized Person.

To confirm that your contractor is a Registered Onsite Wastewater Practitioner see the list of registrants maintained by the Applied Science Technologists and Technicians of British Columbia. To find a Registered Professional see the list provided by the Association of Professional Engineers of British Columbia.

Operating and maintaining systems

Basic septic tank/drainage field systems require little operation and maintenance. If not abused, these systems operate themselves. Unfortunately there are many misconceptions about what is good or bad for a system. See “Do’s and Don’ts”.

More complex systems that have been installed to address specific site conditions may require more attention. An “Authorized Person” should be engaged to develop and implement an operation and maintenance plan.



For more information contact the Public Health Office of the Interior Health Authority at:

South Cariboo Health Centre
Bag 399, 555 Cedar Avenue
100 Mile House, BC V0K 2E0
Phone: 250-395-7676

or visit their website.

The Sewerage System Standard Practice Manual (, 1.3 MByte), issued by the BC Ministry of Health in September 2006 is a valuable reference for the design, installation and maintenance of sewerage systems as defined by the Sewerage System Regulation (2004), that all Registered Onsite Wastewater Practitioners have to follow.

If you are looking for information about your existing wastewater treatment system, you can obtain copies of the original permit or certificate information from the above office.

If you can’t find your septic tank and drainage field see this pamphlet (PDF, 4 pages, 1.5 MByte) produced by the BC Ministry of Environment.