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Designing a rainwater storage system

You might have already read that it is monsoon season here and we have plenty of water flowing, but the dry weather always returns and with it severe drought in parts of the island. While I can always turn on the tap to water the rooftop planters, others are not so lucky. My husband, a marketing manager for mosquito coils, once told me of his sales representatives being turned away from remote territories because the people desperately needed the trucks to bring in water, not consumer goods. Because of this I feel compelled to make the most of the rain we are receiving here in Colombo and make it last through the dry spells. This is where my exploration into rain water storage begins.

Rainwater systems

The simplest and most popular system is a small barrel or garbage can positioned under a gutter downspout with a tap near the bottom to attach a garden hose. These are great for getting started, the casual user, or a home with many downspouts and garden to be watered all around the home. The water can easily be distributed and little construction has to be done to install the system.

However, storage capacity can be limited with the single-barrel approach and our home is built right up against two others, limiting the number of downspouts and external storage space.

Another approach is to use large IBCs or water tanks at a single downspout. Storage capacity is greatly increased and the user gains more water pressure (at least when the tank is fairly full). But again, these are unsuitable for our use as we have only one major downspout near our garden space, and only a narrow space between stairs and the back of the house to position the rain water storage.

These considerations brought me to a third system, daisy-chaining multiple barrels. One barrel serves as the main input, but several other barrels are linked with tubing in a way that allows the barrels to fill at the same time and somewhat equally. This would allow us to use narrower barrels that fit in our space but still increase capacity. In theory, an unlimited number of barrels could be linked and rainwater storage capacity increased as finances and space allow.

Home economics

A quick word on the economy of installing a rain barrel system – it should make sense financially as much as ecologically/ethically.

To be honest, water is not expensive here. We pay monthly, at most, $4 USD for water service. So while it might make sense for my parents who spend $100 or more per month on water service in Southern USA to invest in a large tank intended specifically for water storage, it makes no sense for us here in Colombo.

Many containers can be salvaged and re-purposed to hold rain water. As long as the water is only being applied to the garden, most containers should be fine. However, any water intended for filtering and use by the home or animals should be stored in clean containers which have not previously held any toxic substances. If you have access to them, look for used pickle, olive, and other food barrels in your area.

I am finding that in Colombo most containers do not go to waste and few re-usable containers are simply given away. I love the frugality of our community, but it does make it difficult to find cheap and safe containers for our purposes. Because I would like to eventually add filtration and pump the rainwater to our main tank for household use (cutting our annual water expenses to $0) I am opting for new trash bins when building our system. They are less expensive than any of the used food-grade barrels I have come across but will still allow us to expand when it makes financial sense to do so.

System components

Now that we know which materials we can reasonably use, we have to account for all the necessary components in a hands-off system. I do not want to have to constantly monitor the rains, flush the lines, or get in trouble with the authorities for breeding dengue-ridden mosquitoes (a real problem here).

The essential components of a system are a tank for rainwater storage, a downspout for input, an overflow pipe, and a tap for easily accessing the stored water. Another component we will include in our system is a multi-layer filtration and mosquito prevention top. This will consist of window screen, cotton or muslin for filtering fine particles, and hardware cloth for strength. While the water inlet will be small, this screening layer will cover the entire top of the main barrel, underneath the lid, to prevent any mosquitoes from coming in. The overflow pipe will connect directly to the original remains of the downspout which flow to a septic tank to further prevent mosquito breeding opportunities.

Flexible tubing will also be purchased to link the barrels, as well as taps for water access.

The system pictured at right is the best model I have found that will work in our space. The forum to which it links also gives a good breakdown of how it was constructed.

My goal is to make a smaller version of this system to start, keeping the costs below $50 USD to match our annual water expenses.

Continue to follow along to find out whether we can completely offset our water bill!

Margie is the founder of IG and is passionate about the therapeutic benefits of working with nature in the garden. She enjoys mangosteen, the rainy season, hammocks, and wild visitors in the garden.

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