In my rainwater harvesting presentations, I mention a little device called the Uniseal(R). They might be found at RV suppliers & Hydroponic or Aquaponic stores, but you can also order them from RainCollectionSupplies.com or click here to go directly to the Uniseal page.

These can be easily used to make rain barrels from recycled drums and all work can be done from the outside of a closed top drum! Make sure you have the right size bit for the size you order.

Rainwater Harvesting Basics at the Texas Solar Energy Society 2008 Renewable Energy Roundup.

Parts 2-5 of the above "Basics" presentation above are available on YouTube or follow the links listed below:
An updated version is available for your event or workshop.
Part 2: http://www.youtube.com/watch?v=PP2zgwGHMkc&feature=related
Part 3: http://www.youtube.com/watch?v=pdXTkLgP7Cs&feature=related
Part 4: http://www.youtube.com/watch?v=VYzzix-7_4s&feature=related
Part 5: http://www.youtube.com/watch?v=ulzVANZMdmU&feature=related
For the 2010 Roundup, I presented a Build-A-Barrel Workshop, but video is not available.

If you are planning a whole-house potable water supply, filtration and UV purification is required. My experience shows the easiest method is a complete kit such as the Trojan UV Max™ IHS12-D4 Integrated Home Ultraviolet System. It features a 10" 5 Micron Sediment Pre-filter, a 20" 5 Micron Carbon Block Filter and comes with 3/4" Connections. Shipping is included. Clink on the Technical Specifications tab to download a PDF of the performance features. This system has a timer for the UV light that reminds you to purchase the Replacement Lamp for UVMax systems each year. You can search for all the different parts of this system separately if you wish, but the easiest hook up is with the complete kit from my supplier, RainCollectionSupplies.com.
Replacement filters are available, click on filter

Rainwater Diagram
This diagram was originally created (in Microsoft Word!) years ago when I was at the City of Austin Water Conservation Division. Later, it was revised when I was with Austin Energy Green Building. Since I still use it in presentations and workshops, and I am constantly asked if it is available on the Web, I uploaded a version. A pdf version is available upon request as long as the attribution remains as illustrated below.