Introduction to domestic roofwater harvesting
A sufficient, clean drinking water supply is essential to life but millions of people throughout the world continue to not have access to this basic necessity. After decades of work by governments and organisations to bring potable water to the poorer people of the world, the situation is still dire. The reasons are many and varied:
- Many of the world's poor simply cannot afford the capital intensive and technically complex water supply systems which are widely promoted by governments and agencies throughout the world
- Communal schemes suffer from a inadequate maintenance due to a lack of knowledge, skill or money
- Water supplies can become polluted either through industrial or human wastes or by intrusion of minerals such as arsenic or fluoride
- The growth in water need is outstripping available supply resulting in spring damage, dropping water tables and depleted reservoirs
Roofwater or rainwater harvesting (RWH) is an option which has been adopted in many areas of the world where conventional water supply systems have failed to meet the needs of the people. It is a technique which has been used since antiquity and examples of RWH systems can be found in all the great civilisations throughout history. The technology can be as simple or as complex as required. Traditionally, in Uganda and in Sri Lanka rainwater is collected from trees, using banana leaves or stems as temporary gutters; up to 200 litres may be collected from a large tree in a single storm. With the growth in corrugated iron roofing in many developing countries, people often place a small container under their eaves to collect falling water during a storm;. one 20 litre container of clean water captured from the roof can save a walk of many kilometres to the nearest clean water source. In the industrialised countries of the world, sophisticated RWH systems have been developed with the aim of reducing water bills or to meet the needs of remote communities or individual households in arid regions. Many individuals and groups have taken the initiative and developed a wide variety of different RWH systems throughout the world.
It is worth bearing in mind, however, that Domestic Rainwater Harvesting (DRWH) is not the definitive answer to household water problems. There is a complex set of interrelated circumstances which have to be considered when choosing the appropriate water source. Cost, climate, technology, hydrology, social and political elements all play a role in the eventual choice of water supply scheme which is adopted for a given situation. RWH is only one possible choice, but one which is often overlooked by planners, engineers and builders. The reason that RWH is rarely considered is often simply due to lack of information – both technical and otherwise. In many areas where RWH has been introduced as part of a wider drinking water supply programme, it was at first unpopular, simply because little was known about the technology by the end users. In most of these cases the technology has quickly gained popularity as the user realises the benefits of a clean, reliable water source at the home. In many cases RWH has been introduced as part of an integrated water supply system, where the town supply is unreliable or where local water sources dry up for a part of the year, but is also often used as the sole water source for a community or household. It is a technology which is flexible and adaptable to a very wide variety of conditions, being used in the richest and the poorest societies on our planet, and in the wettest and the driest regions of the world.
T.H. Thomas and D.B. Martinson
Roofwater Harvesting: a Handbook for Practitioners
Bound copies and free pdf dowload available from the publishers site