Great books often take some time to come together. Professor Datta and I first spoke in December 2014 and it has taken four years for his book to reach publication. Very sadly, Professor Datta passed away in August 2018, before he saw this book published. However, the book text was completed and his project has now come to fruition.

This is a book of which his family can be proud; it is a treasure trove of information that will prove incredibly helpful to water management students, academics and professionals worldwide. It is truly a fitting testament to his 40 years in the sector.

The World Bank in 2014 noted:

‘Water is one of the most basic human needs. With impacts on agriculture, education, energy, health, gender equity, and livelihood, water management underlies the most basic development challenges. Water is under unprecedented pressures as growing populations and economies demand more of it. Practically every development challenge of the 21st century – food security, managing rapid urbanization, energy security, environmental protection, adapting to climate change – requires urgent attention to water resources management.

Yet already, groundwater is being depleted faster than it is being replenished and worsening water quality degrades the environment and adds to costs. The pressures on water resources are expected to worsen because of climate change. There is ample evidence that climate change will increase hydrologic variability, resulting in extreme weather events such as droughts floods, and major storms. It will continue to have a profound impact on economies, health, lives, and livelihoods. The poorest people will suffer most.’

It is clear there are numerous challenges in water management in the 21^st Century. In the 20^th Century, most elements of water management had their own distinct set of organisations, skill sets, preferred approaches and professionals. The overlying issue of industrial pollution of water resources was managed from a ‘point source’ perspective.

However, it has become accepted that water management has to be seen from a holistic viewpoint and managed in an integrated manner. Our current key challenges include:

• The impact of climate change on water management, its many facets and challenges – extreme weather, developing resilience, storm‐water management, future development and risks to infrastructure
• Implementing river basin/watershed/catchment management in a way that is effective and deliverable
• Water management and food and energy security
• The policy, legislation and regulatory framework that is required to rise to these challenges
• Social aspects of water management – equitable use and allocation of water resources, the potential for ‘water wars’, stakeholder engagement, valuing water and the ecosystems that depend upon it

This series highlights cutting‐edge material in the global water management sector from a practitioner as well as an academic viewpoint. The issues covered in this series are of critical interest to advanced level undergraduates and Masters Students as well as industry, investors and the media.

Globally, the recent past in human history has seen increasing demands on the Earth’s limited water resources due to the ever‐growing population, urbanization, agriculture intensification, and competition for economic aspirations. Use of groundwater resources has also changed dramatically due to emerging new technologies, mechanization, specialization, and government policies that favor maximizing developmental activities and production. Although these changes have had many positive effects, there have also been negative impacts, such as unplanned indiscriminate overexploitation of groundwater leading to decline in water level; degradation of land, soil, and water resources at an alarming rate; loss of biological diversity; indiscriminate waste disposal, etc. With global demand for groundwater projected to outstrip supply by 2030, many areas may face water insecurity. Groundwater managers have relied largely on supply‐side infrastructural projects, which are environmentally, economically, and politically expensive, and also create political tensions due to intra‐ and interstate administrative and political boundaries.

Water harvesting has been practiced successfully for millennia in some parts of the world. The principle of rainwater harvesting is essentially to capture high‐intensity rainfall causing potentially damaging runoff from areas of low water‐holding capacity, and using this for plant irrigation and/or water supply in areas where rainfall is limited, uneven or unreliable with frequent dry spells. Management of groundwater resources includes ensuring its assessment and development, and protection from depletion and degradation, for maximizing the environmental, economic, and social benefits of its equitable availability, integrated with improving its supply and consumption efficiency, economic efficiency to sustain investments and operations, and waste management. However, water harvesting potential, in reality, remains largely unknown, unacknowledged, and underappreciated.

This book provides an overview of proven good practice in rainwater harvesting all over the world, which can be adjusted to the local context, and forms a practical reference guide for the integration of water harvesting technologies into the planning and design of projects. It will inform planners, decision makers, and practitioners in the field for use at watershed and river basin level. For the first time, this book attempts to uncover, collate, and make available current knowledge about water harvesting technologies, and the settings in which they tend to perform best. On a broader scale, the book is intended to facilitate and disseminate good practice in water harvesting to local and regional planners/advisors, rural development consultants, rainwater harvesting networks and communities, project managers, extension agents, and other relevant staff.

In the twenty‐first century, the projected global demand for water is expected to outstrip supply due to the impacts of rapid growth in population, urbanization, agricultural intensification, industrialization and economic aspirations. Increasing water availability in terms of quantity, maintenance of water quality, and water security has become a focus of increasing international concern. Generally, to meet increased demands for water, water managers have relied on large‐scale, supply‐side infrastructural projects, such as dams and reservoirs, which are environmentally, economically, and politically costly. However, with the vast majority of water resources being transboundary, crossing intra‐ and interstate administrative and political boundaries, and often being ignored or taken for granted, supply‐side projects can create political tensions. Hence, during the last three decades or so, for managing the water demand–supply gap for survival of humans, animals, and plants, the importance of rainwater and groundwater in the development process has been increasingly recognized.

Flexible approaches to policies and planning all over the world in the 1960s–1980s resulted in a revolution in the agricultural sector, the largest user of water resources. In spite of these commendable efforts, much remains to be done to use rainwater and groundwater resources optimally and efficiently on a sustainable basis because availability of these resources is fixed and supply is diminishing very rapidly, generally due to increasing demand and abuse. Water demand management involves, in particular, improving water harvesting and conservation, use and reuse to ensure water availability during times of both normal and atypical conditions, through the communication of innovative ideas, norms, and methods for water conservation and encouraging society to reduce water consumption by changes in practices and attitudes towards water resources. To communicate the value of groundwater resources, it is essential to examine their occurrence, conservation, distribution, consumption, and use for domestic, agricultural, and other purposes.

In our rapidly urbanizing world, access to groundwater resources is not only inadequate in many areas but also highly unsustainable. Unplanned exploitation of groundwater has been alleged to be responsible for water scarcity in many parts of the world, although scientific knowledge to support such a contention is limited. Hence, effective sustainable groundwater resources management requires a clear understanding of the linkages between various resources in a natural setting. The large infrastructure market and growing need for water supply intervention is attracting the interest of international development agencies, multinational corporations, and investors. Private sector involvement as a proposed mode to address this problem appears to be politically contentious. As shortages of resources occur and technology develops, so do their technical, economic, and environmental complexities.

My attitudes have been formed and opinions shaped by the steady accumulation of evidence and examples during my 40‐year professional career, undertaking extensive field investigations in the context of the Groundwater Recharge Assessment and Management, International Hydrological Program (IHP, UNESCO), the Asian Regional Co‐ordination Committee on Hydrology, Agricultural Research and Development, and Environmental Impacts Analysis. I have had the opportunity to analyze national and international academic work and review reports and policy documents on natural resources in the political and historical landscapes underlying global water resources demand, supply, and consumption. I believe that all the alternatives and their potential costs and benefits need to be carefully evaluated based on sound knowledge of the resources and related aspects before any final decision can be taken. Continued scarcity and degradation of water complicated by the variability and intensity of weather patterns has become an increasingly serious concern.

For example, in India, due to increasing population and multisectoral demand for water resources, water supply is multidimensional, linked to reliable assessment of availability, scope for distribution, augmentation, reuse or recycling, and protection from depletion and degradation. There is an urgent need to protect groundwater quantity and quality from depletion and ensure its optimal utilization. However, in India (global champion of groundwater abstraction), as over 70% of surface water resources are polluted, groundwater supports >80% of water supplies and 60–90% of irrigated agriculture, although groundwater is also polluted in many parts. In much of the north‐west region, there has been shallow groundwater renewal from limited modern recharge over the past decades and by interaction with lakes and rivers. In most places, low annual recharge (<5–11% of rainfall) to shallow groundwater suggests a limited renewal potential of the dynamic component.

Since the hydrogeological, social, economic, cultural, and political factors vary greatly at regional and local scales and the aggregate impact of millions of individual decisions is difficult to assess, no single template for management can be developed. Due to diminishing water supply over recent decades, efforts on better harvesting, conservation, and reuse of resources have been taking place to improve the way resources are used for industry, agriculture, and domestic purposes. However, in the context of water governance, the rules and responsibilities are divided between central and state authorities and ineffective management has resulted in conflicts among different sectors. To reduce water consumption and wasteful utilization, practical measures should include strict regulation of groundwater extraction and waste discharge into water bodies, identification of pollution sources and containment of pollution spreading from known sources, development of vulnerability maps, and conservation of floodwater in floodplain aquifers.

For rainwater harvesting to ensure sustainable groundwater supply, development and management must be based on adequate knowledge of groundwater systems, considering environmental, geographical, economic, social, and political aspects. Practical decisions should be governed by ethical values (honesty, trust, reliability, transparency, etc.), giving more importance to citizens’ welfare and economic development than to private interests.

The public services reform programs focus on administrative policy and legalities but overlook governance arrangements. Policy discourse has only recently started to consider governance of water supply as a key issue. The technologies are considered as an important dimension in the design of supply systems. The widespread use of groundwater creates a vast supplement to consumption, and is important for financial, economic, and ecological sustainability of supply. However, groundwater use is mediated by economic and political power via social and technological systems, to keep tariffs very low by not increasing coverage. Thus, it is more readily available to powerful groups, leading to depletion in the overall resource and negative effects for poorer users and the hydrological system as a whole.

In this context, even though the title of this book refers specifically to rainwater harvesting and groundwater management, it intends to add to the literature considerably beyond both, extending to what water harvesting exactly means, overview of the historical evolution of water harvesting for groundwater recharge; benefits and gaps in knowledge; implementation and funding strategies; public participation; and the strengths, weaknesses, opportunities, and threats of the harvesting technologies. Although emerging threats are dynamic and diverse, efforts can be made to address the issues and also to analyze the extent to which artificial recharge approaches have been successful in finding solutions to water scarcity problems.

Chapter 1 aims to provide general information and understanding of the issues, concept, and principles of rainwater harvesting and water security; food‐water‐energy nexus; climate and environmental impacts (floods and droughts); and discusses the challenges in achieving groundwater security. Chapter 2 outlines mega‐trends of growth in population, urbanization, agricultural and economic aspirations; increased demand for water, food, and energy; and anticipated climate change that can affect water security. Chapter 3 describes basic information on groundwater provenance, occurrence, availability, recharge, residence time, pollution characteristics; identification of recharge zones vulnerable to floods; and risk mitigation. Chapter 4 describes historical phases of water harvesting systems; artificial groundwater recharge; its local benefits and achievements so far; possible negative impacts; governance problems; and to what extent water harvesting by artificial recharge technologies can help to solve water scarcity. Chapter 5 provides international scenario and global case studies of water harvesting in selected countries with differing climates, incomes, and lifestyles; and successes and failures of water harvesting for groundwater recharge.

Chapter 6 highlights SWOT analysis of water harvesting systems; strengths, weaknesses, opportunities, and threats; and issues/limitations/questions that need attention. Chapter 7 describes challenges associated with water harvesting; land encroachment, land grabbing, water pollution, etc.; and risks associated with managed aquifer recharge. Chapter 8 covers scope of water harvesting for groundwater management strategies; background of GWM; artificial recharging methods; requirements of sustainable integrated water resources management; good governance in solving sustainability challenges; demand management tools to achieve groundwater resource conservation targets; performance of governance in transition, legal, and policy frameworks.

Chapter 9 describes guidelines to make water harvesting helpful and meaningful for GWM; demand management framework, and tools for groundwater resources managers. Chapter 10 deals with future scope; policy framework; integrating ethical principles with management; and presents proposed ways to move forward in a collaborative, co‐operative way to develop policies for sustained supplies, by modifying the attitudes and behavior of all users in order to balance demand with supply and avoid costly expansions to achieve natural resources sustainability for the supply network – the costs being economic, environmental, and political.

This book is distinctive in the sense that (i) there is currently no proper international definition of rainwater harvesting for groundwater management; (ii) it is difficult to extend the limited research conducted so far to sustainable groundwater management at the river basin scale and the actual processes that enable the application of GWM; (iii) while the definitions of water management tend to focus on flood, waste, and potable water collection, treatment, and distribution, the concept embraces little on the impact of water use on the natural ecosystem, making it difficult to demonstrate or compare RWH successes across areas; and (iv) an understanding of the social, economic, and political dimensions of demand for water lags significantly behind science and engineering knowledge on supply of water. This book will provide guidance to administrative, academic, and research interests and help to raise public awareness on ethical values in the effective use of water harvesting approaches for groundwater recharge, and the risks associated with managed aquifer recharge.

First and foremost, I thank the Almighty’s grace for enriching me with the power to believe more and more in my passion for water and to march forward for my dreams, and for making me realize how true this gift of book writing is for me, and for inspiration and motivation to continue to improve my knowledge and progress in my professional career. I thank and appreciate my wife Shakuntala and son Ankur for always standing beside me, making me feel happy to follow my ambitions, and for having the patience with me for taking on another challenge that decreases the amount of time I can spend with them. I also thank all my co‐workers during my professional career, for allowing me the freedom to manage projects and provide the necessary time and resources which gave me the opportunity to think about the theme of this book. I appreciate that they believed in me to provide the leadership and knowledge which made this book a reality.

This book would not have been possible without the continuing interest of Justin Taberham, Publications and Environment Consultant, Series Editor and Advisor for Wiley Publishing and Palgrave Macmillan/Springer Nature, from the beginning. I thank Justin Taberham; Andrew Harrison, Senior Commissioning Editor, Earth and Environmental Sciences; Athira Menon, Project Editor; Anabella Talbot, Senior Editorial Assistant, all of John Wiley & Sons Publishing, Oxford, UK, for their continuing interest, and devoting time and effort to providing excellent support and advice to bring this book to the present stage. I would like to express my gratitude to all the John Wiley & Sons publishing community who provided support and assistance in the editing, proofreading, and design and helped me to make this book complete.

Last, but definitely not least, I’d like to thank all those colleagues in the Indian central and state authorities and agencies, who have been with me over the course of 40 years during my professional career, and all those in rural areas who helped in the extensive field investigations. Although I cannot mention all their names, discussions with them have been very helpful in obtaining real grassroots knowledge and understanding of rainwater harvesting problems, perspectives, and governance issues related to groundwater assessment and management.