RainCatcher



Summary: When it comes down to large scale restoration with native tree species, water availability is truly a key impediment. Without it, tree mortality is huge, and if you have it, the cost of deploying it to individual trees is commonly prohibited given the scale desire.

RainCatcher is a device developed for the purpose of collecting enough rainwater to irrigate individual trees constantly for as long as the device remains deployed. Also, the device is easy to deploy and affordable. Additionally, it can be reused, which reduce cost of irrigation over time.



Rationale: RainCatcher is one idea being developed to overcome the massive tree mortality we have when planting trees with volunteers. One can easily capitalize on the manpower of volunteers to plant trees, but the needed irrigation after planting remains a critical limitation to unleash the planting potential of people at large.



There are several products available such as Nucleario and Waterboxx, which are inspired in the same idea. Their problem is that they are still not cost-effective for scaling up; as an example, at the time of this post, waterboxx was around $US20. They are for single use, which means the cost is per tree. If you want to plant say 1 million trees, at $20 per device, irrigation alone will cost you 20 million dollars with this method.

Functionality: The principle of RainCatcher is simple. Collect, store and deploy enough rainwater for a tree to be irrigated at all times; this while making the device simple to deploy and affordable.


Lets start with the "Collect" side of the problem. The amount of water that you can collect at any give place is in principle a function of the amount of rainfall and the area over which you collect the rainwater. Using the rainwater catchment calculator, I estimated that for some of the driest of places in Hawaii, one need to collect rainwater over a 10 square feed area to ensure at least 2 litters of water a week.

Now lets move on to the "Store" side of the problem. You may think that if we want to deploy two litters of water a week all year around, then we will need a water container that is large enough to hold at least 104 litters (i.e., 52 weeks times 2 litters a week). However, water storage is a dynamic process because water falls at different times of the year while you constantly take water from the reservoir.

Remarkably, a container that hold at least 50 litters of water will be enough to ensure you will always have water for your tree at two litters a week. Consider, for instance, that if it does not rain for three months straight; under that scenario all you need is a water container with at least 24 litters at the start of the dry spell (two litters for each of twelve weeks). By the time the dry spell finishes, the container will be nearly empty, ready to take on more rainwater.

This consideration is important because you do not want a container that is to small and goes dry, nor to big that you under use it while increasing your costs.

The "Deploy" side of the problem has been addressed in another post.

Development: Reducing costs has been a core consideration while developing RainCatcher.

RainCatcher is simply a plastic bag, with a top/cap that works as a canopy that collects and funnels water into the bag, where the water is stored. The bag is hold in place by a PVC frame. The idea has been to use materials that are cheap and develop a device that can be re-used as to reduce cost of irrigation per tree; the device can be used over the lives of several trees.

The third version of RainCatcher fulfilled the technical requirements of the problem: collect, store and deploy water:


RainCatcher version 3



Unfortunately, I did not take photos of the first two versions, all I have are the stored bags.


RainCatcher Early Versions



While effective at fulfilling the technical requirements of rainwater irrigation, the problem of version 3 was the cost.


Four-way join for RainCatcher version 3.

For this version, I used a custom made join to ensure one could create an inclination in the canopy as to allow water to be funneled into the reservoir.


3D print and mass produced version of four-way join for RainCatcher version 3.

Each of these joins cost $25cents, and we needed four of them. So this part alone was one dollar. Add the cost of the PVC pipes (another $2.5 dollar) plus the cost of the actual catchment bag ($5), and the price tag for this version was already $8.5 dollars.

Field testing of this version also revealed that the corners, where the PVC pipes join with the tent, were prone to breakage after several months.


Tent prone to breakage when in contact with PVC pipe



The solution to this problem was to use a reinforcement with a stronger material in each corner.


Corner reinforcement to avoid canopy breakage



In order to reduce cost of version 3, I replace the four way join for a readily available 5-way join (it costs only $20 cents in Amazon).


Five way join to hold canopy and water tank



And rather than having four bars to keep the tent up, I used only one pipe in the middle. These design changes reduced cost of PVC pipe to just $1 and the cost of the joins to $20 cents as we only needs one join.



The result is RainCatcher version #4:


RainCatcher version 4



It cost $4.5 dollars. The materials have UV light protection and it should last under the elements for up to 15 years.

The problem with version 4 is that it requires the PVC tube in the center to be driven into the soil, as to keep the structure standing up. This tube need to be nearly perfectly vertical; in the opposite, it creates an inclination in the canopy funneling the water towards the edges of the canopy.

I am currently working on alternative versions of RainCatcher, to satisfy two purposes 1) easy to assemble and 2) be very, very, affordable.


Version of RainCatcher for rain and dew collection



This version above requires minimum assembly, provides a benefit for weed control and the canopy is designed to collect dew water. Basically, this version will collect water even if it does not rain. The idea here is that the water tank could create enough temperature differential, for water in the air to condense on the canopy of the tank. The gridded structure will allow for the condensed water to precipitate and be funneled to the tank. I explored the mass production of this version with different suppliers and the best we came out with was $18 per unit using Thermoforming. So, this version is technically pretty nice, but unfeasibly economically. I even modified it such that it can be re-used making the cost per tree lower, but even then, it was not economically viable.




Version of RainCatcher with no assembly required



The version above requires no assembly at all. Just put it by your seedling and done. This will be very convenient to work with volunteers. The problem again was cost. We reviewed the design with several manufacturers and the best we got was $30 per unit using a technique called Rotomolding.




RainCatcher V7



It turns out that one can make a part much cheaper using injection Molding. But the bigger the part, the bigger the mold and the bigger the price tag. So, in the design above, I broke RainCatcher into two components: one is the tank, which does not need to be too big and the canopy, which needs to be broad to collect water over large of an area. The water tank came be done with injection molding at $6 each and the canopy can be made of plastic carton at $70 cents per unit. The price of the mold is $30,000, auch…. This version will also require some assembly.


Inflabable RainCatcher



This version above is the most promising one. It can be put around the tree to control weeds, it has large of an area to collect water and the tank can store up to 50 litters. It is basically, a kid’s inflatable pool with a canopy. It will cost only $1.5 per unit. More on this soon.




RainCatcher is being developed by Camilo Mora. Thanks to Asryelle Mora Rollo and Audrey Rollo for their help doing several of the pilots.