What system do I need for a 1-2 bedroom house?
Building a small home? A useful starting point is a system that can treat around 400 litres of wastewater a day for one bedroom, or 800 litres a day for two bedrooms.
That’s based on allowing for two people per bedroom, each producing around 200 litres of wastewater a day. It includes everything going down the drains: showers, toilets, dishes and washing.
Here’s what that looks like:
|
Your home |
People allowed for |
Wastewater per day |
|
One bedroom |
2 people |
400 litres |
|
Two bedrooms |
4 people |
800 litres |
These figures give you somewhere to start. Your wastewater designer will check the right allowance for your house, water supply and fittings before choosing a system.
400 vs 800 litre tank
400 and 800 litres is referring to how much wastewater the system needs to deal with each day, rather than the size of the tank itself.
Think of it as two separate questions:
-
How much wastewater can the system treat each day?
-
How much can the tank hold at once?
A conventional septic tank needs space for solids to settle and build up between pump-outs. So the tank holds considerably more than one day’s wastewater.
For example, WaterFlow has a 4,500-litre concrete septic tank. That figure tells you how much it holds, not how much it can treat every day. It also doesn’t mean every small house needs that particular tank.
You don’t need to work out the tank size yourself. Start with the number of bedrooms and let your designer match the equipment to the job.
There are only two of us. Why allow for four people?
Fair question. If you’re building a two-bedroom house for yourself and your partner, allowing for four people might sound a bit generous.
But the wastewater system needs to work for whoever lives there next, too. If you sell to a family who uses both bedrooms, they’ll be having more showers, doing more washing and sending more water down the drains.
The system needs to be ready for that without anyone having to dig up the garden and start again.
That’s why the design normally follows the number of bedrooms, rather than just the people moving in today. Still tell your designer how you’ll actually use the home. They need to choose a system that works well with your everyday use as well as the house’s potential occupancy.
What could work for a one-bedroom home?
A one-bedroom home may be able to use a smaller system designed specifically for lower wastewater flows.
For example, NaturalFlow’s Tiny Home System can treat up to 440 litres a day and is designed for one-bedroom tiny homes and other small-scale uses. Its treatment process doesn’t need electricity, although the site may still need a pump to move wastewater where it needs to go.
It provides what’s called advanced primary treatment. In plain English, that describes how much treatment happens before the wastewater goes out to the disposal field. Your designer needs to check that this level of treatment suits your land.
So yes, there are options made for small homes. The next step is checking which one works on your particular patch.
And what about a two-bedroom home?
Using our example, you’d be looking for a system that can treat around 800 litres a day.
A system rated for 440 litres a day wouldn’t cover that, even if there are only two of you to begin with.
NaturalFlow, BioPod and EconoTreat can all be considered in a size that suits the house. A conventional septic tank may also be an option where the land and treatment requirements allow it.
Two bedrooms don’t automatically point to one particular system. The right choice comes down to your land, how you’ll use the home and how much treatment is needed before the wastewater reaches the soil.
Where does the wastewater go after the tank?
It needs somewhere suitable to go, and that’s where the disposal field comes in.
This is an area of your property set up to spread treated wastewater into the ground. The soil then plays a part in further treatment and absorption.
How much space you need depends on how much wastewater is coming through, how well it has been treated and what the soil can handle. Slopes, groundwater and nearby waterways can affect the design too.
That’s why a small house doesn’t always mean a tiny disposal field. Your soil hasn’t seen the floor plan.
Get this checked before you lock in the driveway, garage and landscaping. It’s much easier to leave the right space on a drawing than move things once they’re built.
What if I want to add another bedroom later?
Tell your designer now, even if it’s only a possibility.
The same goes for a future cottage, granny flat or main house if you’re starting out in a cabin. More bedrooms can mean more wastewater, so it helps to know what the property might eventually look like.
Your designer can work out whether it makes sense to allow for that from the start or plan an upgrade later. That might mean choosing a different system, putting pipes in the right place or keeping some extra land free.
You don’t have to build everything now. A little forward planning just helps avoid paying for the same job twice.
What do I need to get started?
You don’t need to know your tank sizes or have all the technical answers. A few basics will help your designer get going:
- Your house plans: especially the number of bedrooms and bathrooms.
- Your site plan: showing where the house, driveway and other buildings will go.
- Your water supply: whether you’ll use rainwater tanks, a bore or mains water.
- How you’ll use the place: a permanent home, weekend retreat or busy summer bach.
- Any future plans: another bedroom, a second dwelling or a bigger house down the track.
With that information and a look at the site and soil, your designer can work out what you need.
Around 400 litres a day is a useful starting point, allowing for two people at 200 litres each. Your designer will confirm the right figure for your build. Remember, this is how much the system treats each day, not the size of the tank.
Usually around 800 litres a day, allowing for four people at 200 litres each. The final figure needs to be checked for your property before you choose a system.
Not automatically. You’ll probably produce less wastewater day to day, but the system still needs to suit the house if more people live there later. Tell your designer you’ll be living alone so they can take that lighter everyday use into account.
If it isn’t connected to a sewer, the water from its toilet, shower, sinks and washing machine still needs to be dealt with properly. A smaller home may suit a smaller solution, but everything going down the drain still needs somewhere to go.
Ask for a complete wastewater setup for your one- or two-bedroom home, rather than a tank of a particular size.
Make sure the quote explains what’s included: the treatment system, disposal field, installation, any pumps or electrical work, and ongoing servicing.
That gives you a much clearer picture of what you’re paying for and what it will take to keep it running.
