Collecting Rainwater

Dr. Kris,

There’s so much rain it seems a pity not to capture it for use. We erected a gutter on my roof in Ubud to catch the rain water into a rain barrel. The problem is the stored water quickly turns brown and fetid and attracts all kinds of unwanted insect life in there. Can you recommend measures to keep the water clean enough to use for watering plants, maybe washing dishes etc? Not expecting it to be drinkable quality. I have a Nazava filter for that.


Matthew in Ubud

Ah, the wet season in Bali… sometimes the rain can seem like it’s endless – until the dry season comes around again of course, and then you wonder ‘did it ever rain for so long?’

The easiest thing to do would be to put an airtight lid on the barrel or cover it with nylon flyscreen mesh, to keep out the bugs, debris and mosquitoes. I’d be most worried about the mosquitoes, you definitely don’t want to be creating a mosquito farm and all of the unpleasantries that come along with it, the neighbours probably wouldn’t be happy either.

If collecting rainwater in containers, barrels garbage bins etc. make sure you always close off with a lid when it has stopped raining or when it is full of water. Installing a purpose-built water tank would be worth it if planning on longer term use, they’re quite cheap these days. A water storage tank will have a basket to filter out the debris, bugs, soil particles and prevent mosquitoes getting into the tank via the guttering. A tap is installed at the low point on the tank or a small pump can easily be installed for higher water pressure. There should be an overflow valve near the top – you can direct the overflow into another barrel.

Traditionally harvesting rainwater was always a necessity, it’s the best way to conserve water and energy. It is a responsible way to garden for self-sufficiency and conservation but it’s also better for your plants.

Chlorine and other chemicals in tap water raise the pH and essentially ‘lock-out’ nutrients preventing uptake by plants and in this way reducing plant growth and health. Tap water can also contain fluoride, salts, and minerals that are harmful to the soil in the long term. Well-water can also cause problems due to salinity, chemicals and high mineral content.

Rain water usually has a pH close to neutral or slightly acidic, either way rain water is usually softer than both tap and well-water. It doesn’t contain the minerals that are typically responsible for the hard water stains seen on bathroom screens and tubs. This is described as ‘hard’ water and it usually carries a higher pH than rainwater.

Lime-scale encrusted deposits on the inside of hot water kettles is also common sight in Bali – how hard is the tap water here?

Which is an important question as it can cause nutrient lockout, this is a pH level where plants are unable to assimilate the nutrients that are present in the soil. The pH level of rain water is typically more acidic, usually between 5 and 7 and much better suited for nutrient uptake, essentially unlocking nutrients for plants, and it’s also better for the soil and micro-organisms within it.

Rainwater is 100% soft water. Free of the salts, minerals, chemicals, and treatments and that are found in your average town and well-water. Salts and chemicals will build up over time to the detriment of the soil and plants.

Rainwater is slightly acidic. Most plants prefer soil just below neutral pH levels somewhere in the range between 5.5 and 7. Funny that, that rainwater is in a similar, whereas town-water is alkalized to protect the pipes from corroding and can have a pH level upwards of 8.

Rainwater is living water. Stored rainwater will contain organic matter. A rain barrel hosts a beneficial biology supporting micro-organisms and other life. If channelled from your rooftop, there will be traces of organic material, we’re just talking about contact exposure to bacteria, leaf litter, pollen, dust etc. (not surprisingly, great for your plants).

It’s like a light fertilizer every time you water with harvested rainwater along with all the additional organic micro-nutrients!

Rainwater also contains nitrates. A very important macro-nutrient – the most bio-available form of nitrogen -basically it’s dissolved nitrogen and plants love it!

Nitrogen is one of the three essential macro-nutrients that plants need, necessary for development and green foliage. Nitrates, which are made up of nitrogen and oxygen, are formulated by nature for maximum uptake by your plants.

Rainwater is always better than tap water for the garden, its better suited to plant growth and development because of the ideal pH, its soft nature, no added chemicals and the presence of beneficial nutrients, its simply water the way nature intended.

Fresh potable water is valuable resource – rapidly becoming a scarce resource in Bali. A lack of foresight in planning has led to unsustainable harvesting of Bali’s groundwater. There has been ongoing water woes in Bali due to the over-development of the past few decades coupled with the explosive growth of tourism on the island, which has outstripped the capacity of the water resources to keep up. Tapping into the groundwater is unsustainable-it is being used up faster than it can be replenished.

Reports put the capacity of Bali’s groundwater aquifer supplies at around 15-20%.

More often than not wells are drilled on the cheap, without casings or otherwise not up to environmental standards and protocols. This leads to cross contamination from land-based activities, runoff from urban areas, raw sewerage and even chemical by-products from farming such as fertilisers and pesticides. Wells drilled close to coastal areas also risk salt water intrusion. If you could take a cross section of the subterranean ground in the south of Bali with all of the historical drilling that has gone on over the years it may well look more like Swiss cheese than solid rock!

The less water that is used from the local water supply or from wells the better. Each litre of harvested rainwater equals a litre of town or well water that can be conserved or put better use.

We could all do our best to conserve this precious resource a little better. Have a great New Year.


Dr. Kris

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