Water Harvesting Principles

The Water Cycle on Your Site

Every time it rains, water arrives as a gift. The question is whether you capture it or let it leave. In conventional landscapes, water hits hard surfaces, picks up speed, and exits the property, often carrying topsoil with it.

Permaculture reverses this pattern: slow it, spread it, sink it.

Core Principles

Start at the Top

Water harvesting begins at the highest point of your property and works downhill. Roof catchment feeds cisterns. Cisterns overflow into swales. Swales overflow into rain gardens. Each level captures what the one above can't hold.

Slow Before You Store

Moving water is erosive. Before directing water into storage, slow it down with level spreaders, rock lines, or vegetation strips. Slow water infiltrates. Fast water erodes.

Multiple Small Interventions

One massive dam is fragile. Ten small swales are resilient. Distribute your water harvesting across the landscape so no single point bears all the load.

Earthwork Techniques

Swales

A swale is a level ditch on contour, meaning it follows a line of equal elevation across your slope. Water fills the swale evenly and soaks into the soil rather than running downhill.

• Best for: gentle to moderate slopes (2-15%)
• Size: typically 12-18 inches deep, 2-3 feet wide
• Plant the downhill berm with deep-rooted perennials

Rain Gardens

A rain garden is a shallow, planted depression designed to capture and filter runoff. Unlike a swale, it's shaped like a bowl rather than a long trench.

• Best for: capturing roof runoff, driveway runoff, or gutter downspouts
• Size: roughly 20% of the impervious area that feeds it
• Plant with species that tolerate both wet and dry conditions

Hugelkultur Beds

Buried wood logs under raised beds act as long-term water sponges. As the wood decomposes, it holds moisture and releases nutrients over 5-10 years.

• Best for: areas with sandy soil or seasonal drought
• Use logs 4-12 inches in diameter, covered with soil and compost
• Avoid black walnut and cedar (allelopathic)

Roof Catchment Math

A simple formula estimates how much water your roof can capture:

Roof area (sq ft) × rainfall (inches) × 0.623 = gallons captured

A 1,000 sq ft roof in an area with 30 inches of annual rainfall captures roughly 18,700 gallons per year. That's significant.

Use the Water System planner in PatternBase to calculate catchment potential for your specific roof areas and rainfall patterns.

Getting Started

1. Map your water flows during the next heavy rain. Where does water enter, pool, and exit?
2. Start with roof catchment, even a single rain barrel makes a difference
3. Add one swale or rain garden in a problem area where water currently erodes or pools
4. Plant water-loving species in naturally wet areas rather than fighting the moisture

Water is the master resource. Get water right, and many other problems solve themselves.