The Amish collect every raindrop. A 100 m² barn roof with 500 mm rainfall = 50,000 liters/year.
System
Gutter → leaf filter → 200-500 liter barrel. First 5 minutes of rain is dirty (roof dust), need a first flush diverter: first 20-30 liters bypass the barrel.
Filtration
For irrigation: mesh screen is enough. For drinking: sand filter + boiling. Or ceramic filter (Berkey). Amish typically use rainwater for livestock and garden, drinking water from the well.
Storage
Wooden barrel (traditional). Plastic cistern (modern communities). Dark — to prevent algae. Screen on top — against mosquitoes (standing water = malaria).
Winter
Drain before freezing. Ice will burst the barrel. Or flip upside down. Spring — rinse and reconnect.