200-gallon rainwater cistern with gutter connection at the UGA GSI demo site

Stop 8: Cistern

Overview

A cistern is a large-capacity container (typically more than 100 gallons) designed to capture and store rooftop runoff for on-site irrigation or passive stormwater drawdown. Cisterns capture far more water than rain barrels, serving both water conservation and stormwater management goals from larger roof areas.
Practice Type: Rainwater harvesting and storage (large volume)

Quick Facts

Capacity200 gallons (42 in. high x 40 in. wide)
SourceBuilding rooftop via gutters with leaf guards
Drain Port FunctionPassive stormwater drawdown to nearby dry well
Cost Range$1.50 to $7.00 per gallon of storage capacity; $2,000 to $12,000+ total depending on size and type

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.

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 non-potable domestic uses, 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.

How It Works

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.

Design Specifications

System Components

  • 200-gallon capacity cistern (42 in. high x 40 in. wide)
  • Gutter with leaf guard on building roof
  • Downspout pre-filter screen (installed 5 ft. above ground)
  • Hose faucet for manual irrigation access
  • Passive drawdown valve for slow drainage between storms
  • Overflow outlet near top, routed to dry well
  • Stable, level base pad

Try It Yourself

Cisterns are ideal for homeowners with larger roof areas who want to maximize rainwater capture beyond what rain barrels provide. They can be installed above ground, partially buried, or fully underground depending on available space and budget. Above-ground cisterns are the most affordable option and can be connected to drip irrigation systems for automated garden watering.

For Professionals

For commercial and institutional projects, cisterns can be sized to meet specific stormwater management credits under local ordinances. Underground cistern systems offer the largest storage volumes without impacting usable site area. The Georgia Stormwater Management Manual addresses rainwater harvesting systems in its source control practices section.

Resources

Download fact sheets, design guides, and technical resources for this practice.