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Cities may find watering restrictions not as effective as assumed, study says

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When researchers at the University of Waterloo analyzed more than a decade of data from 10 mid-sized Canadian cities that restrict outdoor water use and compared them with five cities that don’t impose limits, they found that restrictions had surprisingly little effect on average summer water use.

Currently, more than 75% of large Canadian cities have some type of summer watering restriction. As municipalities look to adapt to increased risks of urban drought and short-term peaks in water demand, the new study aims to provide an entry point to understanding that watering restrictions are no blanket solution for water conservation, particularly when they aren’t mandatory or no drought exists.

“As the climate warms and the threat of periodic water shortages becomes increasingly prevalent even in water-rich nations, it is critical to better understand seasonal swings in water demand and the ways in which the behavior of urban water users can be influenced by permanent restrictions on certain water uses,” the new study states.

According to the study, Curbing the Summer Surge: Permanent Outdoor Water Use Restrictions in Humid and Semiarid Cities, water demands from 15 selected anonymous cities varied little in general across the climate spectrum they represent, but summer demands were much more variable and could use as much as three times more water in some of the dryer cities analyzed. This led the study’s researchers to concede that water use restrictions can reduce surges in demand when water conservation counts the most.

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“Permanent water use restrictions had little impact on the mean and median water demand during the summer months in both humid and semi-arid cities, irrespective of the stringency of bylaw imposed,” researchers state within the study led by Sara Finley, a University of Waterloo PhD student. “This stands in contrast to previous research evaluating the impact of temporary drought restrictions, which has largely demonstrated that type of policy to be effective in curtailing overall average water use specifically during drought events.”

The 15 participating cities from across five provinces provided a minimum of 13 and a maximum of 25 years of daily water production values for the study.

The study found that permanent water use restrictions may mitigate short-term imbalances between water supply and demand during hot and dry periods, but their efficacy may not extend beyond benefits achieved through temporary restrictions on an emergency basis.

Additionally, the study notes that more research is needed to determine which elements of municipal bylaw restrictions may be most effective in reducing water consumption. Elements such as watering hours, choice of days, promotional effort, and enforcement, each have their own roles to play when it comes to influencing behaviour.

“[…] Those convinced that overall summer demands can be drastically reduced by the introduction of day-of-week watering restrictions may find the result discouraging,” the study states.

Notably, all cities within the study experienced a decline in per capita water demands over the past two decades.

The University of Waterloo study was co-authored by associate professor Nandita Basu.

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