Rain Water Harvesting

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Contents
1 Introduction
2 Need for rainwater harvesting
2.1 Reasons for rainwater harvesting
2.2 Advantages and disadvantages
3 Basic principles of rainwater harvesting
3.1 Definition
3.2 Catchment surface
3.3 Delivery system
3.4 Storage reservoirs
4 Pre-conditions for rainwater harvesting
4.1 Environmental considerations
4.2 Technical aspects
4.3 Water consumption and water management
4.4 Social and gender aspects
4.5 Financial aspects
4.6 Is rainwater harvesting suitable for me?
5 Designing a rainwater harvesting system
5.1 Step 1: Total amount of required and available rainwater 5.2 Step 2: Designing your catchment area
5.3 Step 3: Designing your delivery system
5.4 Step 4: Sizing your storage reservoir
5.5 Step 5: Selection of a suitable storage reservoir design 6 Materials, construction and costs of storage reservoirs
6.1 Selecting the most appropriate storage reservoir
6.2 Available materials and costs
6.3 Water extraction devices and tank overflow
6.4 Description and examples of some rainwater reservoir designs 7 Water quality aspects
7.1 Protecting water quality
7.2 Filters
7.3 First-flush
7.4 Treatment of stored water
8 Usage and maintenance
8.1 Regular maintenance
8.2 Infrequent and annual tasks
Appendix 1: Checklist for construction of storage reservoirs Appendix 2: About RAIN
1 Introduction
Millions of people throughout the world do not have access to clean water for domestic purposes. In many parts of the world conventional piped water is either absent, unreliable or too expensive. One of the biggest challenges of the 21st century is to overcome the growing water shortage. Rainwater harvesting (RWH) has thus regained its importance as a valuable alternative or supplementary water resource, along with more conventional water supply technologies. Much actual or potential water shortages can be relieved if rainwater harvesting is practised more widely. People collect and store rainwater in buckets, tanks, ponds and wells. This is commonly referred to as rainwater harvesting and has been practised for centuries. Rainwater can be used for multiple purposes ranging from irrigating crops to washing, cooking and drinking. Rainwater harvesting is a simple low-cost technique that requires minimum specific expertise or knowledge and offers many benefits. Collected rainwater can supplement other water sources when they become scarce or are of low quality like brackish groundwater or polluted surface water in the rainy season. It also provides a good alternative and replacement in times of drought or when the water table drops and wells go dry. One should, however, realise that rainfall itself cannot be managed. Particularly in arid or semi-arid areas, the prevailing climatic conditions make it of crucial importance to use the limited amount of rainfall as efficiently as possible. The collected rainwater is a valuable supplement that would otherwise be lost by surface run-off or evaporation. During the past decade, RWH has been actively reintroduced by local organisations as an option for increasing access to water in currently underserved areas (rural or urban). Unfortunately decision-makers, planners, engineers and builders often overlook this action. The reason that RWH is rarely considered is often simply due to lack of informa- Introduction 7tion on feasibility both technical and otherwise. During the past decade the technology has, however, quickly regained popularity as users realise the benefits of a relatively clean, reliable and affordable water source at home. In many areas RWH has now been introduced as part of an integrated water supply, where the town water supply is unreliable, or where local water sources dry up for a part of the year. But RWH can also be introduced as the sole water source for communities or households. The technology is flexible and adaptable to a very wide variety of conditions. It is used in the richest and the...
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