The Dee catchment, in common with much of the North East of Scotland, has a high proportion of households using a septic tank to treat household waste water.

A wide variety of designs are available and care should be taken to ensure the suitability and correct installation of the appropriate system, taking into account flow rate and maintenance.

The tank may be installed underground and is typically divided into two connected compartments. Wastewater from the house is collected in pipes and fed to the first compartment where the solids sink to the bottom and form a sludge and lighter materials float to the surface to form a scum. Between these two layers is the liquid portion which contains suspended solid material and dissolved substances. As the first chamber fills, the liquid portion is slowly transferred to the second compartment. Here, naturally occurring anaerobic bacteria digest the material, producing gases which must be vented. The treated liquid portion is then usually discharged to a soakaway, or occasionally direct to a watercourse, via the tank’s outlet pipe.

The effectiveness of the system can be compromised in a variety of ways but by observing the discharge from the tank, the general health of the system can be easily assessed. A light grey colour indicates a healthy tank. If the discharge includes solids, has a bad smell or has a fluffy grey fungus, then some maintenance is required – either the tank needs emptying (usually every 1 – 3 years) or the resident bacteria need a health check. Some simple measures in the house can ensure your tank remains healthy.

• Do - use moderate amounts of mild detergents, washing powder & liquid, bath time preparations and shampoos; try using less than usual for the same results.

• Don’t - flush anything other than human waste and toilet roll; anything else: Bag It & Bin It.

• Don’t – pour grease or cooking oil down the sink, dispose of in the bin.

• Don’t – allow paint, garden or other harsh chemicals into the drain.

• Don’t – connect rainwater drainage, e.g., from guttering, into the pipes to your septic tank.

For more detail on how to look after your septic tank, download this Scottish Water leaflet.

Select this link to see Scottish Water septic tank de-sludging charges.