Sizing a Tank
Statistically, probably because of the abundance of water in Canada, Canadians use more and dirty more water than any other nation in the world.
According to the Environmental Protection Act (EPA), for purposes of computation, a daily sewage flow of 275 litres (61.6 gallons) per person is recommended for tank design to account for the individual share of all types of water use in a house having modern appliances.
No. of Bedrooms Daily Sewage Flow (Litres)
2 or less (4 People) 1100 (242 gallons)
3 (6 People) 1600 (352.4 gallons)
4 (8 People) 2000 (440 gallons)
Over 4 add 300 litres (66 gallons) per bedroom
Septic tanks for residences of up to 5 bedrooms shall have a minimum working capacity in accordance with this table:
No. of Bedrooms Minimum total working capacity
(allows 2 persons per bedroom) |
(litres) |
(gallons) |
2 |
2700 |
594 |
3 |
3600 |
792 |
4/5 |
4500 |
990 |
Note: Where the number of occupants is known and exceeds two times the number of bedrooms, the tank size selected should be that which relates to the next higher number of bedrooms.
If daily sewage flows are 3600 litres (792 gallons) or less, tank capacity shall not be less than twice the daily sewage flow. If daily sewage flow is in excess of 3600 litres (792 gallons), the tank must be no less than 3/4 of the daily sewage flow plus 4500 litres (990 gallons).
In larger tanks a maximum depth of 1800 to 2000 millimetres (70 to 78″) is recommended. A ratio of length to width such that the length is 2 to 3 times the width is recommended for good proportions.
Computation of the daily sewage flow to be used in design of the sewage system is most important. An applicant for approval of a sewage system should discuss with the approving authority prior to commencing design. Agreement should be reached on the total daily sewage flow, on the average of daily sewage flow where it varies from day to day, and on the flow pattern within peak days.
Certified tanks only are to be used. Manufacturers have strict regulations to follow, and are certified by the CSA or the Underwriter’s Laboratories of Canada.