Harvesting Fog and Dew for Drinking Water and Vegetable Garden Irrigation

With natural water supplies drying up and disappearing and areas affected by drought increasing in acreage every day, learning how to harvest all available atomized water from the air is important.

Alternative forms of irrigation for green roofs and living walls can sometimes be the primary irrigation source for rooftop plants.  We use air conditioning condensate and dew catchers on many of the green roofs we design.

This morning our lanai screen was covered in water droplets though there was not a cloud anywhere to be seen in the sky, a reminder of the available irrigation potential.

Dew available for Green Roof Irrigation

Additionally, a quick early morning walk through the garden offered up the opportunity to see dew droplets all across the vegetable leaves and other plants.

Dew available for irrigation in the garden

Dew can be an important source of 'free' irrigation.  Learning how to harvest the condensed water vapor is easy, as humans have been tapping this resource for ages.

Check out the TreeHugger article here for an informative look at how dew catchers provide drinking and irrigation water to some of Peru's underdeveloped areas.

Then check out an amazing YouTube video showing the construction of a DIY dew catcher!

Always consider dew as an irrigation source when designing vertical green in the Urban Core.

Nature Irrigated Green Roofs and Dew Catchers

Green Roof irrigation, dew and alternative irrigation has been the topic of the last several posts.

And I have come to a realization today.  I've been referring to green roofs designed as fully sustainable units requiring zero mankind provided irrigation as 'non-irrigated' green roofs.

Studying the dew catchers opened my eyes to the proper term for green roofs that do not have additional mankind provided irrigation.

'Nature irrigated green roofs' is the proper term.

Today I want to share a photo of a very effective, cheap to make and made from 100% post consumer recycled materials - Dew Catcher.

Yes, this simple dew catcher is highly effective.


A system of these dew catchers for a green roof or even an Urban Permaculture garden somewhere could save thousands and thousands of gallons of potable water from being used as irrigation water.

15 milliliters of water was collected from the dew catcher shown below on October 18th, 2010 at 8:00 am.

The dew catcher was placed on a piece of plastic wrap and set on a western exposure roof.

20 milliliters does not sound like much at first glance.  However by placing 100 of the dew catchers (no cost - only your time and effort) you would collect approximately 2000 milliliters per morning.

2000 milliliters is equivalent to approximately 1/2 gallon, so you ask - 1/2 gallon - so what?

If you place one dew catcher per square foot then a ten thousand square foot roof would harvest approximately 50 gallons of water every morning where the dew point is sufficient for harvesting.

As we mentioned in earlier blogs, cooler months facilitate the formation of dew.  Here in north Florida, as well as in many other world locations, cooler months are also the months where precipitation amounts are significantly reduced.

So just when the green roof needs additional water the most, nature provides dew.

50 gallons of irrigation water saved over hundreds of thousands of square feet of green roofs and gardens adds up to alot of water saved.  Stewardship.

And possibly the key to understanding the proper design of a self-sustaining Nature Irrigated Green Roof.

So here is the photo.

Urban Permaculture Dew Catcher - Irrigation for Green Roofs

Basic design is the top cut off of a plastic water bottle and slit down the side.

Arguments the unstable plastic will photo-degrade and leach plastics into the roof are probably valid, however there are plenty of other UV stabilized PPE's that would work just as well.

Recycled glass is another option as well as certain fabrics.

The important issue to remember though is that with a little ingenuity we can harvest air laden humidity and create sustainable irrigation systems if we choose.

50 gallons per day on a 10,000 SF roof offers 15,000 gallons per year potential.

Dew Catchers - Nature Irrigated Green Roofs!

As always, Email us with your questions here.

Happy Green Roofing!

Kevin

Green Roof Irrigation and Dew Catchers - 5 Important Factors

Irrigation provided by nature exists and understanding how dew works can make the  Florida (or Arid Locale) Green Roof successful.

Here in North Florida we are in the middle of an on-going three and a half week drought with no rain in sight.

You put water in the birdbath and the water has evaporated by the middle of the day.

Our Urban Permaculture Garden is growing just fine but craves water.

We are abiding by the watering restrictions we have in place here set by the St. Johns River Water Management District.

Yet look at the following photo my daughter took early in the morning!  There was water everywhere, especially on the green roof plants!

Irrigating Green Roof Plants - Dew Catchers

The amount of available water for plants is truly amazing.

We have noticed several interesting factors:

1. Dew occurs early in the morning - before the sun gets too hot and evaporation occurs
2. Early morning dew allows more water to be adsorbed by the plants.
3. Waxy plant leaves - those typically found on recommended green roof plants - encourage the condensed dew to roll off the leaves into the root area soil.
4. Many plant leaves seem to possess a natural form that directs dew to the middle of the leaf, down the stem and onto the root area.
5. Dew seems to be most prevelant during dryer, cooler periods - and those factors correspond exactly with our dry season.
6. The amount of dew is significant, as much as drip irrigation may produce.

So Mother Nature is offering up alternative irrigation means.

And we here in Florida and across the world have a water supply crisis.

Again, I ask - why are we irrigating Green Roofs with costly potable water that truly has a high carbon footprint?

When Mother Nature offers irrigation up for free.

Over the next couple of days I want to discuss dew catcher design and nutrients found in both dew and rainwater.

Happy Green Roofing!

As always - email me with your questions and dont forget to check out Dave Hillary's Free Green Roof Mini-Course.

Kevin

Green Roof Irrigation System - Can Nature Support a Green Roof?

Green roof irrigation can be accomplished via recycled rainwater pumped up from a cistern, potable water supply, a combination of recycled rainwater and potable water or from mother nature alone.

Importantly, a green roof should look good and not dry.  A dry roof could be a potential fire hazard.  Remember how those dry Christmas trees would burn.  Of course, some - like Ducks Unlimited - used to burn their green roofs annually - but most of us would not want to burn a green roof.

Other reasons for keeping the plants watered on a roof include;
1. More photosynthetic activity - hence more CO2 uptake and more O2 production,
2. Greater wildlife habitat,
3. Increased nutrient uptake
4. and others.

However there are also valid reasons for not irrigating a roof.

There is a water crisis here in Florida and across the southeastern US.  Remember the water wars of Alabama, Georgia and Florida a couple years ago?

50% of all potable water usage is typically consumed via landscape irrigation use!  Over withdrawal of aquifer reserves causes sinkholes to develop, wells to go dry and contamination of existing supplies to increase.  Native plantings are encouraged and water reuse is a municipal practice on the increase.

Additionally, roof leakage is a serious concern.  Creating roofs that can withstand a pond-like body of water is expensive and may cause mold problems.

Mechanical systems, including irrigation systems are always subject to eventual failure.  If the irrigation system goes down and the plants are used to significant watering then they may quickly die.

If the system is hooked up to potable water then a flood may occur.

Maybe there are other alternatives.  In our opinion, with the rush to implement new stormwater rules and nutrient removal criteria in Florida, the FDEP and certain testing organizations have jumped to the conclusion that the only way a green roof can survive periods of little to no rain is to install irrigation.

A quick review of Florida literature results in few if any research articles considering alternative irrigation methods.

Granted, FDEP's new applicant handbook suggests using rainwater cisterns to recycle rainwater as an irrigation supply for vegetated roofs, however this is but a selling point for their lack of research on non-irrigated systems and also is seriously flawed.

Suggesting rainwater cistern and rainwater recycling is low impact development is wrong.  Here in Florida half the year approximately sees only minimal rainfall amounts.  Today we are well behind - ten inches or so in our average annual rainfall amounts.  That means all those vegetated roof plants so used to plenty of rainwater irrigation from the cistern are now going to have to be irrigated with potable water or reuse water because they are not acclimated to the dry periods.  This philosophy is 'Anti-Florida Friendly Landscaping' and is a scam.

Certainly there is room for having stormwater volume and retention on the roof and in cisterns, but this approach cannot be the only sanctioned approach for green roofs in Florida.  And because FDEP and various educational institutions are pushing the 'Stormwater Pond on a Roof' approach the Florida Green Roof Industry has to adsorb and deal with the results of those misguided efforts.

Back to green roof irrigation.

Certain nations, such as Australia, New Zealand and others are stepping up and conducting serious research on alternative irrigation systems such as utilization of dew and air humidity.

We should too.

Here in Jacksonville we haven't had rain in three weeks.  Our yards and gardens are dry as a bone.  I'm sure many of the irrigated green roofs around the state are pumping out potable water (all the stored rainwater is used up by now) to keep the green roof plants irrigated.

Check out the following early morning photos.  remember - no rain here in the past three weeks however early morning water is everywhere.

Green Roof irrigation alternative - collect morning dew

Green Roof irrigation alternative - collect morning dew

Green Roof irrigation alternative - collect morning dew

Check out the article on dew collection found at http://www.inhabitat.com/2008/06/26/harvest-water-from-the-air-with-fog-dew-collectors/  

Possibly the research topic of an inspiring student or professor, the potential is great and the market place calls out for such inventions.

Green roof design already has taken advantage of the potential of harvesting dew for irrigation, MetroVerde utilizes compact dew catchers around many green roof plants in the field, harvesting significant early morning water for the plants.

Moreover, early morning water is captured on a more efficient basis by green roof plants because high daytime temperatures and evaporation process have not begun in the A.M hours.

So remember, next time someone says "Green Roofs in Florida Must be Irrigated", pause and ask yourself - has this person really done their homework or are they trying to push an agenda past you without your knowledge.


As always, feel free to contact us via email.

Happy Green Roofing,

Kevin!