Rooftop Harvesting

According to a South African case study, "Small, local solutions can crack water crises"

Before you get started on any project, always be careful to check your local legal codes and policies. Some types of water harvesting are forbidden in certain places for a variety of reasons. 

North America

You may also be interested in reading about:

Learn about which activities use the most water, to develope a plan on curring your own water footprint. In many cases consuming less will have a greater impact than harvesting water, though water collection may be your first step in your water conservation journey.

How safe is roof-water to drink?

Types of Rooftop Harvesting 

There are several ways to harvest water on a roof, these include:

These work with two different methods.

Air Conditioner Drip

One simple and cheap way to harvest water if you already own or work in a place with an air conditioner, is to divert the condensed water that drips out into a flower pot or flower bed.

Life Expectancy: A portable AC unit may only last 5-10 years, while a home unit is expected to last 20-25 years if properly maintained.

Pro: Simple solution of diverting condensed water to plants or a container, instead of letting it go to waste or causing damage to any structures it might drip on.

Con: Relies on a functioning air conditioner, which costs money, and produces dangerous emissions: both air pollutants as well as excess heat.

Solution: Switch to a green energy provider if possible to reduce emissions, and try to supplement your water harvesting options, so you don't have to rely on an A/C for the small amount of water it provides.

Fuel Types: Electricity and refrigerants which act as green house gases.

Blue Roofs 

"In the past, blue roofs were conceived as storage tanks for rainwater harvesting. Today, they form part of SuDS best practice and are designed to facilitate controlled attenuation following heavy rainfall or storms. Blue roofs are suitable for a wide range of building types from domestic to commercial. They place storm water attenuation within the building footprint, making them ideal for urban environments where ground space is limited. Blue roofs can be situated above the waterproofing membrane in a warm roof system or above the water flow-reducing layer in an inverted application, at both roof and podium levels. There is a case to be made that green roofs are a form of blue roof, because they hold water and control run-off; but green roofs cannot do this in a truly controlled way such that the attenuation capacity can be relied upon to be available for a statistically derived storm event. Specifiers may like to consider the hybrid blue/green roof, which combines the aesthetic and ecological benefits of a green roof, with the high-performance water-attenuating properties of a blue roof." - https://architecturetoday.co.uk/roofing-in-detail-blue-roofs-best-practice/ 

Life Expectancy: 10-25 years, but some components made from certain materials can last 50-100 years. Green Roofs are expected to survive for 40-50 years.

Pro: Captures precipitation that might have otherwise contributed to run off and flooding.

Con: Relies on precipitation, meaning it may be unreliable in drier climates.

Solution: People who receive seasonal rain should build ample storage space to help capture as much rain as possible, ensuring more water will be saved for later in the year. They may also want to consider other options such as a well with recharging infrastructure, a grey water system, etc.

Fuel Types: Water Cycle + Gravity

"Green roofs are being increasingly used in urban areas where space constraints limit the use of other stormwater management practices." - EPA: Soak Rain Green Roofs 

Green roofs need to be installed on roofs pitched at no more than 30°. 

These can serve a number of purposes from increasing pollinator or veggie space, to reducing pollution and run off into our water ways. They can even help buildings stay slighter warmer in winter but are better at keeping things cooler in hotter months. According to this source "it is quite common to harvest water from green roofs in Germany and Switzerland." Thought some designs function as zero discharge sites, where "All water is reused within the development, either to irrigate intensive green roofs and landscape at ground level or is used to flush toilets throughout the development." 

Green roofs can absorb up to 70% of the water that lands on them. So if you want to harvest drinkable or reusable water, then these may not be the best choice. However they will still preform the other functions just fine, and are a great solution to helping reduce flooding or run off.

Life Expectancy: 40-50 years.

Pro: Captures precipitation that might have otherwise contributed to run off and flooding. Increases biodiversity. Reduces energy costs associated with heating and cooling buildings. Extends roof life. Reduces emissions not just by reducing energy use, but the plants can sequester greenhouse gases.

Con: Relies on precipitation, meaning it may be unreliable in drier climates. Plants need a small amount of care, including occasional trimming, removal/replacement of dead plants, and removal of invasives. Water collected by these roofs may not be appropriate for drinking or other domestic activities.

Solution: People who receive seasonal rain should build ample storage space to help capture as much rain as possible, ensuring more water will be saved for later in the year. They may also want to consider other options such as a well with recharging infrastructure, a grey water system, etc. Special filtration will be needed if people want to drink water collected from green roofs.

Fuel Types: Water Cycle + Gravity

According to this article "There are three basic types of green roof: intensive (thick), extensive (thin) and semi-extensive (somewhere in between).

Hydropanels

These can be set on the ground or on rooftops.

Source Hydropanels from Zero Mass Water These 350 lb water harvesting panels contain solar panels, an air filter, a mineral cartridge which adds calcium and magnesium, and a 30 liter water collection storage tank, which can be connected to a pipe which can be connected to your home spigot. A 2 Hydro Panel Install can cost between $5,500-$6,500, with shipping from Arizona, USA. The panels can produce up to 8 liters of water per day. They are warrantied for 15 years, and need around $100 of maintenance work every 5 years to replace the air filter and mineral cartridge. There is an app to monitor how the panels are working, for example how much water they are holding. These should work where outside humidity is anywhere above 10%.

Cons: These can be noisy, but have a quiet mode to reduce the fan speed and noise of the fans, but consequently this reduced water production. The mineral packs can also create a strange citrusy flavor, which is said to subside after a few weeks. During freezes the panels go into hibernation, which turns off the pumps and completely stops access to the drinking water.

Life Expectancy: Warrantied for 15 years with repairs/maintenance ever 5 years at roughly $100 per service.

Pro: Uses sunlight and atmospheric humidity to condense water out of air.

Con: Requires solar energy, meaning they may not work during the night or in cloudy weather. Requires humidity, so may not work properly in particularly dry climates.

Solution: Consider pairing this system with back-up options such as rain barrels, a grey water system, and/or a well with ground recharging infrastructure.

Fuel Types: Solar Panels

Additional Equipment

Rain Barrels/Butts & Cisterns 

How to Install a Rain Barrel in Under an Hour, for Less Than $200 This step by step guide encourages you to check your planned installation site before buying parts and getting started, so you can find out ahead of time if the area is unsuitable for any reason (for example slope, plants, pipes or other things). Uses US metrics.

How To Install A Water Butt Explains solutions to attractive vs functional design needs, including for small gardens. Uses standard metrics/Non-US. Includes tips for maximizing your water savings while watering plants.

How To Install Your Rain Barrel (PDF) simple diagrams and instructions for installing a barrel and what the important parts of the barrel are (in case you are making your own) from the Conservation Foundation

Rain Barrels and Cisterns Described the practical features and functions of each, talks about material options, and includes helpful diagrams. Provided by the Low Impact Development (LID) Urban Design Tools Website 

Life Expectancy: 20 years.

Pro: Safely stores rain or grey water for later use.

Con: An turn into a breeding ground for mosquitoes, or be contaminated with dead animals that can fall/get trapped inside. I've found dead frogs who might have hatched but not been able to get out. Dead leaves can build up, leaching tannins into the water.

Solution: Install fixtures that will help keep wildlife and leaves out of the system. Make sure to clean these to prevent plugging and backups. Empty and clean out the container periodically.

Fuel Types: Water Cycle + Gravity

Alternative At-Home Water Harvesting Options

Water Recycling 

Grey Water 

Simple Greywater Systems For Your Home "A greywater system is used to take water that has already been used from places like your laundry, shower and sink and divert it to use in another purpose like watering gardens or landscaping instead of flushing it down into the sewer. Greywater is different from blackwater (aka sewage) because while it may have some residuals like dirt, hair, grease, etc from it’s first use, they aren’t toxic to the environment and the water can be reused in some applications." When using a grey water system for irrigation, it is important to be very careful in choosing "bath soaps, used homemade shampoos and biodegradable dish soap so as not to damage the soil, plants or watershed." Link talks about legal issues, installation costs, and design elements such as filters.

Toilet to Tap Water Recycling

Toilets can use grey water, function without water, or be a source of water depending on the type you choose, and the infrastructure around it. 

Tools & Resources

Landscaping Know-How

This may give ideas for how to capture and redirect water on the land, which can integrate well with rooftop water harvesting.

Organizations

International

Africa

Asia

India

Europe

UK

North America

Mexico

USA

Oceana

South America

Maps

North America

USA

Grants & Funding

Oceana

Australia

Western Australia

Further Reading