There are many resources to help you with planning and maintaining a rainwater catchment system.  Here are some that we recommend:

Farming & Sustainable Development

Beyond More Crop per Drop [PDF: 1.91 MB - Aug 01, 2007]
The International Water Management Institute, along with nine other partners, explores factors driving the water-food-environment situation.  This publication engages readers to think about five key areas for action, including: increasing blue water productivity; increasing green water productivity; increasing access to water resources; balancing water for food & other ecosystem services; & investing in water security to aid poverty alleviation.  These will result in Integrated Water Resources Management (IWRM), capacity building & continued research.

Ferrocement Tanks

Harvesting the Rain: A Construction Manual for Cement Rainwater Jars & Tanks [PDF: 1.21 MB - Sep 21, 2007]
This is a do-it-yourself guide from UNICEF for building ferrocement water jars and tanks with photographs, based on a successful project in Thailand.

Rain Barrels

How to Build a Rain Barrel
This is an overview of how rain barrels can work for garden irrigation, produced by the Maryland Department of Natural Resources.  Also includes instructions on how to build a low-cost rain barrel, as well as some commercial resources.

How to Build a Rain Barrel
This contains a parts shopping list plus detailed instructions and photos for constructing rain barrels for your garden, an overview of the process, benefits, plus a rainfall/rain barrel calculator.  With thanks to DIYers Rebecca & Andre Chesin.

Wildlife

Rainwater Catchment for Range Livestock
This publication helps you to determine how to water your range livestock with rainwater catchment.  Produced by Billy Kniffen, Cooperative Extension Agent, Texas A&M University.