Rainwater Harvest

Location: Wilmington and Hamilton, MA



  • Demonstrate the use of rainwater harvesting systems on a range of properties from small homes to larger institutional settings as a means to conserve potable water while sustaining landscaping.
  • Reduce use of Ipswich watershed groundwater sources for outdoor watering.
  • Quantify the water savings of residents and property managers using rainwater harvesting systems for all or part of their irrigation needs.

Description: Rainwater harvesting systems are designed to capture runoff from rooftops and store the water for nonpotable uses, such as lawn and garden watering. The systems are intended to reduce demand on public water supplies by replacing potable water with rainwater, where appropriate.

This project funded installation of 39 rainwater harvesting systems on residential properties in Wilmington. The systems consisted of a storage tank, a pressure pump to aid in water distribution, a spigot for a hose, and a water meter to measure flow. Two different sizes of storage tanks were installed: 200-gallon tanks (28 systems) and 800-gallon tanks (11 systems).

Additionally, a large-capacity (8,000-gallon) underground storage vault was installed at the Boutwell Elementary School in Wilmington, to supply water for irrigating the adjacent ball field.  When the storage vault is empty, the system automatically switches to a municipal backup system.  Lastly, a 200-gallon system was installed at the Winthrop Elementary School in Hamilton as part of an “Outdoor Classroom” educational program. The system provides water to a 2,000-square-foot butterfly and vegetable garden.  Teachers at the school developed a specific curriculum for the outdoor classroom and the rainwater harvesting system.

Reducing lawn watering, if done throughout the entire Ipswich River watershed, could have a significant impact on river flows. According to the analyses completed for the Ipswich River Watershed Action Plan, lawn watering accounts for 15 to 20 million gallons per day of water use in the watershed. Rainwater harvesting techniques are most beneficial when combined with drought-resistant landscaping techniques to reduce overall irrigation needs of the plants.

Data Collection and Analysis:
The water meters attached to each rainwater harvesting system provided data on the volume of rainwater pumped from the storage tanks for outdoor use. In addition, the Wilmington Water Department records on each residential participant’s domestic water use were analyzed to compare domestic water demand before and after installation of the rainwater harvesting system.

Project Photos



  • Installation of 200-gallon and 800-gallon residential rainwater harvesting tanks, November 2005
  • Installation of 200-gallon system at “Outdoor Classroom” at Winthrop Elementary School in Hamilton, September 2006
  • Installation of 8,000-gallon underground system at Boutwell Elementary School in Wilmington, April 2007
  • Collection of monthly flow-meter data from residential systems indicating quantities of harvested rainwater used by participants: April 2006 to October 2006 and April 2007 to October 2007
  • Season kick-off meetings for residential participants: June 2006 and April 2007
  • Project close-out meeting with residential participants, May 2008. Attendants celebrated the conclusion of the data collection, listened to preliminary study results, filled out feedback surveys, and heard tips on eco-friendly landscaping techniques.


Costs:            200-gallon systems: $1,375 each

                      800-gallon systems: $3,440 each

                      8,000-gallon underground vault: $23,000

Key Results and Conclusions:

  • Rainwater was used for outdoor purposes by all participants.  Survey results indicate that, in general, the rainwater that participants used replaced the use of domestic water.  However, statistically significant reductions in domestic water use after installation of the rainwater harvesting systems were not discernible, because the monthly volumes of rainwater used were very small compared to domestic water use.
  • The 800-gallon systems yielded an average of 440 gallons/month, while the 200-gallon systems yielded an average of 200 gallons/month.
  • The volumes yielded by the 800-gallon systems represented approximately 20% of the rain that drained to the system in 2006 and 50% of the rain that drained to the system in 2007.  The remainder of the rainfall was lost to overflow, due to storage limitations.  The difference between the two years might be attributable to differences in the way the storms were distributed over the two summers.
  • The volumes yielded by the 200-gallon system represented approximately 14% of the rain that drained to the system in 2006 and 28% of the rain that drained to the system in 2007.  These smaller systems resulted in more loss to overflow than occurred with the larger 800-gallon systems.
  • A weather-based simulation indicated that the 8,000-gallon system at the school could yield approximately 23,000 gallons per month and could supply 79% of the irrigation need of the adjacent ball field.
  • Selecting the appropriate storage size helps balance costs and benefits of rainwater harvesting.
  •   Rainwater Sizing Efficiency Graph  pdf format of Rainwater Sizing Efficiency Graph
illustrating the relationship between storage size and % demand that can be met at the Boutwell School, based on modeling.

Final Reports and Publications:

Tsai, Yushiou, Sara Cohen, Richard M. Vogel, 2011. The Impacts of Water Conservation Strategies on Water Use: Four Case Studies. Journal of the American Water Resources Association. pp.1-15 (print publication pending)  pdf format of The Impacts of Water Conservation Strategies on Water


Ipswich River Targeted Watershed Grant Fact Sheet: Four Water Conservation Case Studies  pdf format of Ipswich River Targeted Watershed Grant Fact Sheet


In-kind cooperation:

  • Town of Wilmington
  • The Winthrop Elementary School in Hamilton

Design and Installation: Rainwater Recovery, Inc., Waltham, MA


Monitoring and Analysis: DCR and Tufts University with oversight from a Technical Advisory Committee comprised of eight water conservation professionals; domestic water use records provided by the Wilmington Water Department