
In an era where water conservation is critical, home scale rainwater harvesting has emerged as a resourceful and sustainable method of collecting water. As the climate crisis and the world’s increasing population put strain on conventional water sources, rainwater harvesting presents a practical solution to reducing this pressure. It also provides homeowners an opportunity to become self sufficient and independent from the utility supply.
By utilizing this resource, you can supplement your home’s water supply while simultaneously reducing your household’s environmental impact and effectively conserving water. You may even be able to fully supply your home with safe, clean water.
In this detailed article, we will guide you through the fundamental aspects of rainwater harvesting systems, including the different options available, environmental factors, key components, important considerations, and more! Keep reading to uncover how this solution for water management can play a central role in ensuring your home is more sustainable and self sufficient.
You may find our Rooftop Rainwater Harvesting Calculator useful while you consider the the information in this article. It will help you determine how much water you will be able to generate from your roof.
Table of Contents
What is A Rainwater Harvesting System Design?
A rooftop rainwater harvesting system is a system that enables homeowners to collect rainwater and store it for later use. Depending on your local regulations and roof type, this may be full potable use, including drinking water, or non-potable use only, such as landscape irrigation systems, flushing toilets, outdoor cleaning, and so forth. Either way, by using rainwater, you can reduce your household’s reliance on its municipal water supply, therefore lowering your town supplied water consumption and reducing water bills.

Here’s a breakdown of how a rainwater harvesting system works:
- Collection: The first step in a rainwater collection system is collecting rainwater, typically from your home’s roof surface. Rainwater falls on the roof and is conveyed, via a gutter and downspout (downpipe) system to a collection point.
- Screening: Before harvested rainwater can be stored and used, it must be screened to remove any debris. This will ensure the water quality is clean enough for its intended use. Filtration is typically carried out through specialized screens or fine mesh filters which catch any particulate or larger material that is in the water.
- Storage: After being screened, the collected rainwater is then stored in barrels or tanks for later use. Rainwater storage vessels can be kept above or beneath the ground, depending on your home’s layout and design preferences.
- Distribution: Stored rainwater is distributed to supply your pressure water system. It may may feed the entire house supply, or it may be a separate system used for non-potable applications. Distribution can be carried out via a pressurized pump system or a gravity-fed system. Remember, a utility supply is typically no less than around 15 metres or 50 feet of pressure and your rainwater tank will likely supply a lot less than that. Without careful design you therefore can’t connect the two systems together.
- Overflow and scour: You must consider both the overflow and scour (for tank cleaning) of your rainwater harvesting tank and ensure it is diverted back into the stormwater system (either disposed of onsite, or into the municipal stormwater system). From
- Maintenance: To ensure your rainwater collection system works efficiently, you must carry out routine maintenance. This involves cleaning screens, regularly checking for leaks, and occasionally treating collected rainwater to ensure its quality. Tanks also require ‘scouring’. That is, from time to time, if sediment builds up in the tank you must open a valve at the bottom and allow it to flush the tank.
Types of Rainwater Harvesting Systems
There are many variations on the theme of rainwater harvesting systems suited to different household needs. Familiarizing with the various designs available will aid your search for (and design of) the right one. Here are some common rainwater harvesting system types worth exploring:
Rain Barrel or Water Butt
Suited To: Homeowners with limited outdoor space

A rain barrel, also known as a water butt, is a simple rainwater harvesting system that collects rainwater from roof downspouts into a barrel-shaped vessel. Rain barrels are well-suited to urban, residential settings and are primarily utilized for outdoor watering, such as landscape irrigation.
These compact yet effective systems are straightforward to install and cost-effective, making them ideal for inexperienced individuals and homes with limited outdoor space.
‘Dry’ System
Suited To: Standard homes
A ‘dry’ rainwater collection system, also known as a direct catchment system, collects rainwater from rooftops and directs it to a storage tank via a direct, gravity fed pipeline. At no point does the pipeline become charged full of water. This is the most common type of rainwater harvesting system and suits most homes with minimum maintenance requirements.
‘Wet’ System
Suited To: Larger homes and commercial buildings
A ‘wet’ rainwater harvesting system, known as indirect catchment, or charged systems, collects rainwater from rooftops and directs it to an above-ground storage tank. The pipeline between the roof and the tank is typcially taken to the ground and then rises to the inlet of the tank. It is ‘charged’ and must be designed such that it can be drained at the low point to avoid the accumulation of sediment in the pipeline.
Sub-Surface Storage and Irrigation
Suited To: Agricultural land
Sub-surface water storage and irrigation can be effective for capturing and dispositng of large quantities of rainwater runoff, enabling it to seep into the ground. In doing so you recharge the aquafer and can infact use the ground to store water for future agricultural use.
This method of rainwater harvesting is popular among agriculturalists in some areas, as it maintains a steady supply of water in the ground, ensuring plants and soil are sufficiently hydrated. In some cases the water is extracted from the ground to supply irrigation and other agricultural uses.
Stormwater Planters (Bioswales)
Suited To: Homes in urban environments, particularly areas with runoff issues
Stormwater planters, also known as bioswales, are specially landscaped areas purposefully designed to capture, filter, and store rainwater. They contain plants and soil that collectively absorb water and remove pollutants to enhance water quality.
These highly absorbent systems help reduce flooding risks by managing excess water and are notably sustainable thanks to their use of plants and soil. This makes them ideal for homes in urban areas, especially those with runoff issues.
Gravity Supply System
Suited To: Homes with elevation differences.

A gravity-based rainwater harvesting system depends utilises gravity to distribute collected rainwater without a pump. This method of rainwater harvesting typically involves positioning storage tanks so they are elevated, to encourage water to flow downward to desired points of distribution. If you have steep land, perhaps you install your rainwater harvesting system on a shed higher up the hill (for example).
These systems don’t require automated pumps and therefore present minimal running costs, making them budget-friendly, yet impressively effective.
The Benefits of Using a Rainwater Harvesting System
From effective water conservation to reduced water bills, rainwater harvesting systems are beneficial in a number of ways. Here are some of the key benefits you can experience by installing a rainwater harvesting system:
Water Conservation
By using harnessing the rainwater that falls on your roof, you can reduce your household’s demand on conventional water sources. This just makes sense! Rainwater harvesting is an effective way of conserving precious water resources.
This is particularly beneficial to those who occasionally experience water scarcity, or the rest us that may in the future! Rainwater harvesting increases your home’s resilience water shortages.
Environmentally Friendliness
Because rainwater harvesting systems lessen your dependence on utility water supplies, they significantly reduce the energy and resources needed to distribute and treat water from traditional sources, such as reservoirs. This helps limit your household’s carbon footprint.
Reduced Water Bills
Rainwater harvesting offsets your demand on the utility supply, and therefore reduces your water bills, making your overall cost of living more affordable.
Financial Incentives
Individuals who install rainwater harvesting systems could be eligible for various financial incentives, including rebate programs and tax exemptions.
This will drastically reduce the expense of purchasing and emplacing the structure, therefore making a rainwater harvesting system more affordable. Inquire with your local government to see whether you could be eligible for any relevant financial incentives.
The Key Components of a Rainwater Harvesting System Design
When building a new rainwater harvesting system, it’s essential to ensure you fully understand the key components that comprise these systems, any avoid any difficult plumbing surprises when do the install.

- Catchment Area: This is the collection area, typically your roof.
- Gutter System: This transfers rainwater from the roof to downspouts.
- Downspouts (downpipes): These direct rainwater from gutters to the filtration or screening system and storage tanks.
- First Flush Diverters: These divert the initially collected rainwater away from storage tanks to ensure the water collected is clean. This is typically the first 1mm of rain that falls on the roof which may be highly contaminated.
- Filtration Systems: This includes filters, screens, and is some cases, more sophisticated treatment systems which remove debris and contaminants from rainwater to ensure it is safe and clean enough for use. For most systems, a simple screen on the top of the tank will be adequate.
- Storage: These store collected rainwater for later use and can be inground or above ground tanks, built from steel, concrete, fibreglass, plastic or other water retaining material suitable for water storage.
- Distribution System: This sends harvested rainwater to the point of use. This may be full potable house supply, if appropriate, or non-potable uses such as in the garden.
- Overflow Pipe: This diverts excess rainwater away from systems to prevent storage tanks from overfilling during heavier rainfall. They should be plumbed into a stormwater system.
- Scour: This enables the tank to be drained from the lowest point, to allow accumulated sediment to be cleared.
Important Rainwater Harvesting System Design Considerations
In order to fortify an effective rainwater harvesting system, there are some key design considerations to acknowledge.
First, it’s important to assess your household’s water demand and general usage patterns. This will help you understand how much rainwater you need to harvest, and determine an appropriately sized tank that will meet these requirements. You may want to use our Household Water Usage Calculator to estimate your household’s water demand.
Your usage through day, week or month will go up and down, but a large tank will allow you to buffer out those peaks and ensure you have water when you need it. Sizing your tank is an important step and will depend on the rainfall patterns in your area. You should seek out relevant data to inform this decision. The following websites will assist:
- In Australia, go to the Bureau of Meteorology website.
- In the UK, go to the Met Office website.
- In the USA, go to the National Weather Service website.
- You may also find useful information on the World Bank Group Climate Change Knowledge Portal.
As a rule of thumb, tanks to provide full household supply may range from 5000 to 10 000 US Gallons (20 000 to 40 000 litres).

From the data, try to understand the frequency of rain events, and the longest likely period without rain. Then, using the Rooftop Rainwater Harvesting Calculator, you’ll be able to decide how much rainwater storage you should have to ensure you will not run out. Of course, you may choose to have a smaller storage, or your rooftop may simply be too small, but you’ll now understand your rainwater harvesting potential.
Once you have sized your tank, and directed roof runoff to it, you must consider how the water is used and if a booster pump is required. There are also tank overflow and scour considerations that you must design for. These pipes must be installed and directed to an appropriate stormwater disposal location such as your road side drainage or other stormwater infrastructure.
Your budget is another essential consideration. By acknowledging the expenses of purchasing, installing, and maintaining a rainwater harvesting system, you can create a realistic budget. It’s also worth exploring whether your government offers relevant incentives or rebates, to make your project more affordable.
Finally, before installation, you should also check whether your local authorities require any specific permits or enforce any relevant restrictions related to rainwater harvesting, to ensure your project is compliant.
FAQs
What Is the Simplest Design?
If possible, keep things simple. Take full advantage of gravity to avoid pumps and keep your downspouts flowing (i.e. not ‘wet’ or ‘charged’).
That is, downspouts to gravitate into storages without holding water, and then supply your demand via gravity also (no pumps).
This will minimise maintenance and future problems.
What Is the Cheapest Way of Harvesting Rainwater?
The most affordable way of harvesting rainwater is through rain barrels, also known as water butts. These simple yet effective above-ground containers can be placed beneath downspouts to collect and store rainwater. This solution is cost-effective and easy to install, making it ideal for beginners and those with tight budgets.
Perfect for offsetting water usage in your garden!
Is Collected Rainwater Safe To Drink?
Collected rainwater maybe suitable for drinking, but it also may not be. This is dependent on your rooftop material; risk of contamination from the roof; air quality; acid rain potential etc. Unless you are sure of these things, we suggest taking the careful approach and using harvested rainwater for various non-potable uses, such as watering your plants, cleaning your laundry, flushing toilets, and so forth.
You can always seek the advice from your local authority and, if they advise potable rainwater harvesting is OK, go right ahead!
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