So far this summer at least 22 communities south of Boston have limited residents' water use, despite a rainier-than-average July.
Summer rains have little effect on the fundamental calculus that leads to water restrictions. The precipitation evaporates, gets absorbed by plants, and runs down storm-water drains in torrential bursts, having less effect on water supply than in other seasons. And in many communities, residents use significantly more water in the summer.
Dedham, Duxbury, Kingston, Norwell, Pembroke, Plymouth, and Westwood all had voluntary restrictions as of July 31, according to the state Department of Environmental Protection. That means residents were asked to limit watering to certain hours of the day, or alternate days of the week.
Mandatory restrictions, requiring residents to follow limitations on out side watering, or complete prohibitions, were in effect in 15 communities: They include: Abington, Braintree, Bridgewater, Foxborough, Halifax, Hanover, Hanson, Mansfield, Marion, Middleborough, Raynham, Rockland, Sharon, Walpole, and Wareham.
Outdoor watering restrictions go into effect because "demand exceeds pump capacity," said Richard Clark, superintendent of the Halifax Water Department.
Mandatory restrictions ban sprinklers in Halifax. Without such restrictions, Clark said, constant pumping of well water could stress the system and compromise water quality.
In most cases, officials said, the reasons for restrictions relate to infrastructure rather than supply. Ground water may be abundant because of rain, but a municipal water system only has only so many wells, tanks, or reservoirs. In Bridgewater, which gets its water from a well system, a mandatory outdoor watering restriction bans all but hand-held watering in order to keep enough water on hand for fire protection.