HSTP Systems explained

by | Dec 20, 2023 | Advice & inspiration, Building basics & regulations

Sewage systems aren’t what most homeowners are most excited to talk about with their new homes. However, how you plan to deal with this is an essential consideration to any new home build (after all, the alternative is pretty grim). Home Sewage Treatment Plants have gained popularity in recent years, but what are they exactly and how do they differ from other systems on the market? That’s exactly what we’re going to explore in this article. We’ll look at what HSTP systems are, their pros and cons and how to calculate the right size septic system for your property.

What are HSTP systems?

HSTP stands for Home Sewage Treatment Plants and is a decentralised wastewater treatment system used in residential homes, small communities, or smaller-scale commercial sites. In the most basic terms, it is a domestic version of a sewerage plant. The overall purpose of a Home Sewage Treatment plant is to treat and purify wastewater, greywater, and blackwater without using dangerous chemicals and with an overall goal of reducing environmental impact.

A home sewage treatment system will receive and provide wastewater treatment to all of the following:

  • Kitchen (sinks, dishwasher, etc)
  • Bathroom (shower, bath, sinks, toilet)
  • Laundry (washing machines and sinks)

How does this differ from other systems?

The overall idea of an HSTP system is that it provides an eco-friendly solution to treat wastewater. The treatment process relies on naturally occurring bacteria to break down matter to create treated water safely into the environment.

Advantages and Disadvantages of an HSTP System


  • A more environmentally friendly option
  • Treats grey water and black water.
  • Cost-effective with reasonable running costs.
  • Can treat grey water at a higher rate than a septic tank
  • Can recycle water for irrigation, thereby cutting down on water bills.


  • More expensive to purchase and install than a septic system.
  • Requires more approvals for installation.
  • Higher running costs than septic tanks, as HSTPs require electricity.
  • Limited capacity. HSTP systems tend to be smaller than regular septic tanks.

What are the different components of a HSTP system?

Below is a diagram outlining the typical parts of an HSTP system.

How do HSTP systems work?

Below is an outline of how an HSTP system tends to work. While there may be some systems that work differently, the below outline applies to most systems.

Wastewater collection: Treatment systems collect all household wastewater from bathrooms, kitchens and laundries.

Primary Treatment: The primary chamber is where the first round of treating wastewater happens. Solids are separated from liquids through filtration and sedimentation. This septic tank is where solids settle to the bottom and the water rises.

Secondary treatment: The partially treated wastewater from the septic system is further treated in an aeration or treatment chamber. Aerobic bacteria and microorganisms will break down organic matter into wastewater that can be safely discharged.

Tertiary treatment: This is an optional step that won’t be included in every HTSP system. In some situations though, it may be required to have an additional step to help treat the wastewater.

Effluent Discharge: Once the process is complete, the treated wastewater or effluent will be disposed of into the environment. The exact discharge method will vary depending on the make and model of your system, but some variants include mounds, absorption trenches, or subsurface irrigation.

How much do HSTP systems cost?

There is a wide range of options available on the market, so depending on the type and size of the system you’re buying, prices will vary. Our research indicates a system will cost anywhere between $2,000-$9,000. Factors that will affect your installation price will include your soil type and the slope of your land.

How to determine the HSTP system size for your new build?

The better you can estimate your needs, the easier it’ll be to purchase the right size system for your needs. Here are some steps that will help:

  1. Determine how many people the system will need to accommodate. If you’re building an investment property or aren’t sure, you can calculate by bedrooms. For a house with three bedrooms, you’ll want a system that can accommodate five people. For each additional bedroom add one to amount of people your system needs to accommodate (for example, for four bedrooms, get a 6p system, five bedrooms, 7p, etc).
  2. Calculate the number of litres you produce per day. One person is estimated to produce 150 L of water so multiply this number by the number of people in your home (for example, 4 x 150 =600L)
  3. Whatever number you get from the above calculation, add 2000L. So using the above numbers, 2000 + 600 = 2600

Are there any regulations around HSTP system installation I need to be aware of?

As with most features of your house, there are regulations concerning sewerage systems. When it comes to HSTP systems specifically, local councils tend to have their own specific guidelines and regulations, so it’s always worth checking in with the local council in the area you’re planning to build. While we can’t vouch for every single suburb in Australia (there are quite a few), most guidelines and regulations will cover the following points:

  • the types of household wastewater systems allowed to be installed
  • minimum requirements of any potential system
  • the permits and approvals you’ll need and how to obtain them
  • installation requirements and guidelines
  • maintenance requirements.

Our quick tips when choosing an HSTP system

  • Make you purchase an HSTP system size that can accommodate your needs. A too-large system means you’ll needlessly spend money. As for the downside to purchasing too small a sewerage system, we’ll leave that to your imagination.
  • Check with the local council about guidelines and regulations so you have a thorough understanding of what is feasible on your property. Talking to a local expert will also help in this regard.
  • Some of the key factors to consider when choosing your HSTP include budget, the size of your home, your property’s soil type, and whether you’re on a sloping block.

Buildi is here to help with your new home!

The type of septic system you install is just one of many decisions you’ll need to make during your home-building journey. Buildi is here to help guide you through the entire process. From finding the best builder for your project to helping you during negotiations, we’ll ensure you save money, time and stress.

Book a free, impartial consultation with us today!


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