A cistern is a large-capacity container (typically 100 gallons or more) designed to capture and store rooftop runoff for on-site irrigation or passive stormwater drawdown. Unlike rain barrels, cisterns can harvest and store significant volumes of water from larger roof areas, serving both water conservation and stormwater management goals.

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The Problem:
Large roof areas generate substantial volumes of stormwater during rain events—far more than rain barrels can capture. Without a storage system, this water becomes runoff that contributes to erosion, flooding, and water quality degradation. At the same time, landscape irrigation accounts for a significant portion of residential and institutional water use, drawing on treated municipal supplies.
The Solution:
Cisterns bridge the gap between small rain barrel collection and engineered stormwater detention systems. They capture rooftop runoff in volumes meaningful enough to supply supplemental irrigation or to significantly reduce the stormwater contribution from a building. When configured for passive drawdown, cisterns empty slowly between storms, ensuring storage capacity is available for the next rain event while directing water to an infiltration area.
Pre-Filtration
Effective pre-filtration is essential for cistern longevity and water quality. The demonstration site uses a two-stage approach: gutter guards prevent leaves and large debris from entering the downspout system, and a self-cleaning downspout filter screen removes finer particulates before water enters the cistern. Regular inspection of these filters is the most important maintenance task.
Passive Drawdown vs. Irrigation Storage
If the primary goal is stormwater management, a passive drawdown configuration is recommended. The bottom drain valve is left partially open so the cistern slowly empties to a nearby infiltration area (such as a dry well) between storm events. This ensures the cistern has capacity to capture the next rainfall. If the primary goal is irrigation supply, the cistern can be kept full and water drawn manually through the hose faucet as needed. The demonstration site illustrates both functions simultaneously.

See the in Action

At the demonstration site, a 200-gallon cistern collects rooftop runoff from the building via repaired gutters fitted with leaf guards. A downspout pre-filter screen installed 5 feet off the ground removes debris before water enters the cistern. The system features dual outlets: a hose faucet for manual irrigation use and a passive drawdown valve that slowly drains water to the nearby dry well (Stop 9) between rain events. An overflow outlet near the top of the cistern handles excess water during heavy storms, also routing it to the dry well.

Practice Type: Rainwater harvesting and storage (large volume)

Capacity: 200 gallons (42 in. high x 40 in. wide)

Source: Building rooftop via repaired gutters with leaf guards

Dual Function: Irrigation supply and passive stormwater drawdown to nearby dry well

Cost Range: $1.50 to $7.00 per gallon capacity ($2,000–$12,000+ depending on size and type)

Maintenance

Task
Frequency
Details

Downspout filter check

Monthly (more often in fall)

Check self-cleaning downspout filter for clearance; remove accumulated debris

Gutter cleaning

Spring and fall

Clean source gutter and verify leaf guard is secure

Tank flushing

Annually (late winter)

Clean out tank interior; flush to lawn area

Debris inspection

Late fall

Check for buildup of debris at tank bottom; flush if needed

Valve and fitting check

Seasonally

Verify passive drawdown valve is functioning; check all bulkhead fittings for leaks

Mosquito prevention

Ongoing

Ensure all screens are intact and all openings are sealed