Clean water – it’s right above your head

Rain falls unto roofs and then runs off. And then? You could catch it and drink it. Any suitable roof surface—tiles, metal sheets, plastics, but not grass or palm leaf—can be used to intercept the flow of rainwater and provide a household with high-quality drinking water. Rainwater harvesting systems have been used since antiquity, and examples abound in all the great civilizations throughout history.

The groundwater level may be too deep, groundwater may be contaminated with minerals and chemicals such as arsenic or salt, surface water may be contaminated with faeces or chemicals. Rainwater falls on your own roof, and is almost always of excellent quality. It enables people to manage their own water supply and provides the luxury of “water without walking”, relieving the burden of water carrying, particularly for women and children. This convenience is available at every house on which rain falls, whether on a mountain top or an island in a salt sea. It is a truly great idea.

A women using her water storage tank in Guinnee-Bissau. Photo: Paul Akkerman

Storage tanks
Once you catch the water from the roof (or other hard surfaces), you have to store it somewhere. Ferro-cement tanks, made with a layer of cement with steel-wire reinforcement, are usually the best and cheapest option, and can be made locally. When a tank is below ground, it is called a cistern. No idea why, really.

Roof rainwater is usually of good quality and does not require treatment before consumption. The most important thing to ensure water quality is a good lid, keeping out light and insects, and a filter, keeping out all kinds of dirt.

The cheapest tank of all is to use the ground beneath your feet. This is called groundwater recharge, and is simply accomplished by letting rainwater infiltrate in the ground, instead of letting it escape and flow away. When you need it, you pump it up.

As small or large as you want
A rainwater harvesting system might be a 500 cubic meter underground storage tank, serving a whole community. Or it might be just a bucket, standing underneath a roof without a gutter. Each 20 litre container of clean water might save a kilometers long walk to the nearest source of clean water, and as fetching water on cold, wet and slippery days is particularly unpleasant, even this small yield is highly valued. In Uganda and Sri Lanka, rainwater is traditionally collected from trees, using banana leaves or stems as temporary gutters.

It is a technology which is extremely flexible and adaptable to a wide variety of settings, it is used in the richest and poorest societies on the planet, and in the wettest and driest regions of the world. Let’s build more gutters!

Author: Mark Tiele Westra, Editor Akvopedia.

Links:

• Other blogs in the series “Akvo solution of the week”
• For more low-cost water and sanitation solutions, visit Akvopedia, part of akvo.org
• Indian movie by CSE (www.cseindia.org) promoting use of rainwater harvesting
• Akvopedia article on rainwater harvesting
• Wikipedia article on rainwater harvesting
• Download the book “Roofwater Harvesting: A Handbook for Practitioners” from the IRC website
• Rainwaterharvesting.org, Indian website on rainwater harvesting

Roof-harvested rainwater for potable purposes : application of solar collector disinfection (SOCO-DIS)

Amin, M.T. and Han, M.Y. (2009). Roof-harvested rainwater for potable purposes : application of solar collector disinfection (SOCO-DIS). Water research ; vol. 43, no. 20 ; p. 5225-5235. DOI: doi:10.1016/j.watres.2009.08.041

Abstract

The efficiency of solar disinfection (SODIS), recommended by the World Health Organization, has been determined for rainwater disinfection, and potential benefits and limitations discussed. The limitations of SODIS have now been overcome by the use of solar collector disinfection (SOCO-DIS), for potential use of rainwater as a small-scale potable water supply, especially in developing countries. Rainwater samples collected from the underground storage tanks of a rooftop rainwater harvesting (RWH) system were exposed to different conditions of sunlight radiation in 2-L polyethylene terephthalate bottles in a solar collector with rectangular base and reflective open wings. Total and fecal coliforms were used, together with Escherichia coli and heterotrophic plate counts, as basic microbial and indicator organisms of water quality for disinfection efficiency evaluation. In the SOCO-DIS system, disinfection improved by 20–30% compared with the SODIS system, and rainwater was fully disinfected even under moderate weather conditions, due to the effects of concentrated sunlight radiation and the synergistic effects of thermal and optical inactivation. The SOCO-DIS system was optimized based on the collector configuration and the reflective base: an inclined position led to an increased disinfection efficiency of 10–15%. Microbial inactivation increased by 10–20% simply by reducing the initial pH value of the rainwater to 5. High turbidities also affected the SOCO-DIS system; the disinfection efficiency decreased by 10–15%, which indicated that rainwater needed to be filtered before treatment. The problem of microbial regrowth was significantly reduced in the SOCO-DIS system compared with the SODIS system because of residual sunlight effects. Only total coliform regrowth was detected at higher turbidities. The SOCO-DIS system was ineffective only under poor weather conditions, when longer exposure times or other practical means of reducing the pH were required for the treatment of stored rainwater for potable purposes.

Article Outline

1. Introduction
2. Materials and methods

2.1. SODIS and SOCO-DIS systems
2.2. Microbial analysis

3. Results and discussions

3.1. Sampling site and characteristics
3.2. Characteristics of different weather conditions
3.3. The effects of the collector’s base angle and different backing surfaces in the SOCO-DIS system
3.4. Comparison of the SODIS and SOCO-DIS systems

3.4.1. The effects of radiation and temperature effects on microbial inactivation
3.4.2. The effects of initial pH values on disinfection efficiency
3.4.3. The effects of initial turbidity values on disinfection efficiency
3.4.4. Microbial regrowth in SOCO-DIS system and comparison with SODIS

4. Conclusions
Acknowledgements
References

Contact:

• Assistant Professor, Department of Environmental Sciences, COMSATS Institute of Information Technology, Abbottabad, 22060, Pakistan, e-mail: muhammadamin [at] ciit.net.pk
• bProfessor, Civil and Environmental Engineering Department, Seoul National University, Shinrimdong, Kwanak Gu, Seoul, 151-742, Republic of Korea, e-mail: myhan [at] snu.ac.kr

Meteorology: Taming the sky

Is it really possible to stop rain, invoke lightning from the heavens or otherwise manipulate the weather? Jane Qiu and Daniel Cressey report on the once-scorned notion of weather modification.

[...]

China has one of the largest programmes for weather modification in the world. It spends between 400 million yuan (US$60 million) and 700 million yuan a year on it, and employs 32,000 people to operate 35 specially equipped planes, 7,000 anti-aircraft cannons and 5,000 rocket launchers. Official figures from the China Meteorological Administration say that the country created 250 billion tonnes of rain between 1999 and 2006, an annual production of more than 30 billion tonnes. This is enough to meet the needs of more than 500 million of its 1.3 billion people, but the country aims to generate 50 billion tonnes a year by 2010.

Many researchers, both in and outside China, doubt that sufficient evidence has been accumulated to support this claimed success. “In fact, China is very much behind in this area,” says Zhang Hong-fa, an atmospheric scientist at the Cold and Arid Regions Environmental and Engineering Research Institute in Lanzhou. “A false sense of achievement would impede genuine progress.”

Read more: Nature, 453, 970-974 (2008) – doi:10.1038/453970a – Published online 18 June 2008

Beetle-Based Water Harvesting

A pioneering water harvesting system inspired by the Namib Desert Beetle is one the biomimicry innovations that will feature in the first annual edition of Nature’s 100 Best© book. The book is an initiative of ZERI, Biomimicry Guild and the Biomimmicry Institute, in cooperation with IUCN, and UNEP.

The Namib Desert beetle lives in a location that receives a mere half an inch of rain a year yet can harvest water from fogs that blow in gales across the land several mornings each month. A team from the University of Oxford and the UK defense research firm QinetiQ, have designed a surface that mimics the water-attracting bumps and water-shedding valleys on the beetle’s wing scales that allows the insect to collect and funnel droplets thinner than a human hair.

The patchwork surface hinges on small, poppy-seed sized glass spheres in a layer of warm wax that tests show work like the beetle’s wing scales.

Trials have now been carried out to use the beetle film to capture water vapour from cooling towers. Initial tests have shown that the invention can return 10 per cent of lost water and lead to cuts in energy bills for nearby buildings by reducing a city’s heat sink effect.

An estimated 50,000 new water-cooling towers are erected annually and each large system evaporates and loses over 500 million litres.

Other researchers, some with funding from the US Defense Advanced Research Agency, are mimicking the beetle water collection system to develop tents that collect their own water up to surfaces that will ‘mix’ reagents for ‘lab-on-a-chip’ applications.

Source: UNEP, 28 May 2008

Rooftop Rainwater Harvesting Systems

For over 20 years, the Barefoot College, India, has helped rural communities to develop their own rainwater harvesting systems and community-managed water supplies:

· In India, nearly 1300 systems in 17 states with a total storage capacity of 47 million liters provide clean water to over 235,000 school children in remote, rural communities.

· In Afghanistan and 5 countries in Africa, 15 rainwater systems constructed since 2006 with a total storage capacity of 1.5 million liters provide clean water to over 4,200 school children.

In their February 2008 newsletter, the Barefoot College gives an overview of their current rainwater harvesting projects, with links to pictures on the construction of a 100.000 litres rainwater tank in Sierra Leone and General Guidelines for Construction of a Rainwater Harvesting Tank in Schools.