18 May 2024

Rainwater harvesting in urban environments: solutions for limited space

As urbanisation rapidly expands, the space for implementing traditional water catchment systems becomes increasingly scarce. Nonetheless, the need for sustainable water management is more prevalent than ever, particularly in bustling urban environments.

One significant solution to rainwater harvesting in spaces constrained by urbanisation is the installation of green roofs. These systems not only help in retaining and utilising rainwater but also combat the urban heat island effect by providing a cooling effect to buildings.

Moreover, incorporating rain barrels or cisterns into building designs provides another practical solution for urban rainwater harvesting. These storage systems can be seamlessly integrated into the existing infrastructure, making them an ideal option for areas where space is at a premium. They can capture a significant amount of rainfall, reducing the reliance on municipal water supply and promoting a more sustainable approach to water management.

Furthermore, permeable pavements present an innovative way to address the issue of rainwater harvesting in densely populated cities. These surfaces allow rainwater to percolate through the pavement and into the ground, replenishing the groundwater reserves and reducing surface runoff. Permeable pavements can be incorporated into a variety of urban environments, from parking lots to pedestrian walkways, making them a versatile solution for a sustainable urban future.

These solutions, when combined with proper urban planning and community engagement, can transform our cities into sustainable urban landscapes. Rainwater harvesting is not only a practical response to water scarcity issues but also a step towards creating a sustainable and resilient urban environment that is well adapted to future climate uncertainties.

This blog aims to explore the innovative solutions for rainwater harvesting in the context of limited space, shedding light on how we can reconcile environmental sustainability with the spatial constraints of our ever-growing cities.

What is rainwater harvesting and why should we do it in an urban environment

Rainwater harvesting refers to the practice of accumulating and storing rainwater for reuse, instead of letting it run off. In urban environments, this can be particularly beneficial for several reasons.

First, the urban water supply often struggles to meet the demands of growing populations, particularly in areas suffering from frequent droughts or water shortages. By harvesting rainwater, cities can supplement their water supply in a sustainable and eco-friendly way.

Second, rainwater harvesting can significantly reduce the amount of stormwater runoff, which often leads to flooding in urban areas. By capturing rainwater, the volume of runoff that goes into storm drains can be reduced, mitigating flood risks.

Finally, harvested rainwater can be used for different non-potable purposes such as irrigation, toilet flushing, washing cars, or cleaning streets, thereby reducing the demand for treated water. This not only saves water but also reduces energy consumption, as treating and pumping water requires considerable amounts of energy.

Therefore, the concept of rainwater harvesting in an urban setting is not merely an environmental initiative, but also a practical solution for water management and a significant step towards sustainable urban living.

How to set up a rainwater harvesting system for limited space

In setting up a rainwater harvesting system within a limited space, the first step is to identify a suitable location for the rain barrels or tanks. Ideally, this would be under a downspout from the rooftop, which can effectively channel the rainfall towards the barrel.

Secondly, the capacity of the barrels or tanks will be determined by the available space and the estimated water usage. A general guideline is that a 1,000-square-foot roof will collect approximately 600 gallons of rainwater for every inch of rain. You can read more about the amount of rainwater you can collect from your roof in one of our previous posts.

After deciding on the capacity, you'll need to select a barrel or tank made from a suitable material. This is often plastic, but other options include concrete or metal. Make sure whatever material you choose is durable, non-toxic, and resistant to algae growth. Again, you can read more about the different materials for water tanks in a previous post.

Next, install a filtration system at the top of the barrel or tank to filter debris like leaves or twigs. This can help maintain the quality of the collected water. Additionally, a first flush diverter can be installed to discard the initial flow of rainwater that may contain contaminants from the roof. Read more about filtering rainwater.

Once the filtering system is set up, the outlet and overflow pipes need to be installed. The outlet pipe should be fitted near the bottom of the tank to allow for easy access to the harvested rainwater. The overflow pipe, on the other hand, should be positioned near the top of the tank to prevent overflow and potential damage.

Finally, it is recommended to cover the barrel or tank to avoid the accumulation of dirt and prevent mosquitoes from breeding in the water.

Whilst setting up a rainwater harvesting system in limited spaces can be a bit challenging, with careful planning and utilisation of space, it is definitely achievable and can contribute significantly towards sustainable water management in urban areas.

At Smart Water, we are helping to contribute to the increasing demand for rainwater harvesting systems here in New Zealand but also around the world. Our innovative, market-leading water tank level monitoring system provides a wireless water tank management solution with mobile app connectivity, allowing you to manage and monitor the water you harvest from anywhere.

It is solutions like this that are helping people to manage their water more efficiently, understand their daily usage and allowing them to put in place measures to reduce usage whilst at the same time, collecting the rainwater from their property, adding to the overall sustainability and reducing the demand on water treatment and municipal water supply.

Benefits of rainwater harvesting in urban areas

Rainwater harvesting provides a plethora of benefits, particularly in urban areas where water demand is high and resources can be scarce. One of the immediate advantages is the potential for significant cost savings on water bills. Utilising harvested rainwater for non-potable uses such as watering gardens, flushing toilets, or washing vehicles can greatly reduce reliance on the metered municipal supply, thereby saving money.

Secondly, by harnessing rainwater, we can alleviate some of the strain on our municipal water supply system. Urban areas are often densely populated, and demand can outstrip supply, particularly during periods of dry weather. By using rainwater for certain tasks, the pressure on the municipal supply can be reduced, ensuring a more consistent and reliable water source for everyone.

Lastly, rainwater harvesting can contribute to improving the water quality in nearby rivers and streams. When rainwater is allowed to run off directly into rivers and streams, it can lead to increased levels of erosion and carry pollutants that deteriorate water quality. By capturing rainwater, the amount of runoff and consequent pollution can be significantly reduced, leading to healthier rivers and streams.

Rainwater harvesting regulations in urban environments

In urban environments, regulations for rainwater harvesting vary across different countries.

In New Zealand, the Building Act 2004 provides a comprehensive framework for the regulation of building work, the establishment of licensing regimes for building practitioners, and the setting of performance standards for buildings. This legislation recognises rainwater harvesting systems and permits their use for non-potable purposes, such as flushing toilets and garden irrigation. To ensure safety, the harvested rainwater must be clearly identified as non-potable, and the system must be installed by a certified plumber.

In Australia, each state sets its own regulations for rainwater harvesting. However, generally, the installation of rainwater tanks is highly encouraged, especially in urban areas to combat water scarcity. Some states even offer incentives such as rebates or grants to encourage homeowners to install rainwater harvesting systems. Both potable and non-potable uses are permitted, but plumbing regulations must be adhered to, and any system supplying potable water must comply with the Australian Drinking Water Guidelines.

In the USA, regulations vary by state. Some states, like California and Texas, encourage rainwater harvesting and provide incentives for its implementation due to the water scarcity issues they face. In other states, such as Colorado, the practice was initially limited due to old water rights laws but recent legislation has begun to permit residential rainwater collection. It is essential to check local regulations before installing a rainwater harvesting system. You can read more about US legislation across different States when it comes to rainwater harvesting in a previous post.

Additional steps to maximise the benefits of rainwater harvesting

To significantly enhance the efficiency and benefits of rainwater harvesting, several additional steps can be implemented:

a. Planting trees to increase the evapotranspiration rate: Trees play a vital role in the water cycle, drawing up water from the ground and releasing it back into the atmosphere through a process called evapotranspiration. By planting more trees around your property, you can increase the evapotranspiration rate, creating a more balanced and healthier water cycle in your local ecosystem. This, in turn, can provide a supplementary source of water for your harvesting system.

b. Installing green roofs to capture more runoff: Green roofs are covered with vegetation and a growing medium, installed over a waterproofing membrane. They serve multiple purposes such as absorbing rainwater, providing insulation, creating a habitat for wildlife, and helping to lower urban air temperatures. The installation of a green roof can dramatically increase the amount of rainwater captured and utilised, reducing reliance on mains water and making your home more self-sufficient.

c. Constructing swales or berms to slow down stormwater flow rate: Swales and berms are simple and effective landscaping features that can help manage stormwater runoff, prevent erosion, and increase water infiltration. Swales are shallow, wide ditches designed to slow water flow, filter out pollutants, and increase infiltration into the soil. Berms are raised patches of land that can redirect water flow, reducing runoff and increasing water retention in your garden. Incorporating these features into your landscape design can optimize your rainwater harvesting system, making your property more water-efficient.


In conclusion, rainwater harvesting is an incredibly important and often overlooked factor when it comes to sustaining the health of our environment and tackling the effects of the ongoing climate crisis.

Urban areas are particularly high-risk for drought conditions, which can have a major impact on ecosystems and food security.

By making sure that rainwater harvesting is given proper consideration in urban planning we can create more sustainable cities with access to clean water for everyone.

Furthermore, by harnessing the power of natural rainfall systems we can reduce flooding risks and rely less on fossil fuels for irrigation and other water needs.

Harnessing rainwater in urban areas is not only beneficial for the environment but it also provides economic incentives– it helps cities save money on water expenses while creating new job opportunities at the same time.

With well-designed urban infrastructure, communities can ensure that they are prepared for future flooding or vanishing water issues.