NORTHAMPTON — The city joined dozens of other communities across the commonwealth when it enacted its water use restriction Friday, though only a small fraction of those are in western Massachusetts.

The water use restriction began on June 15 and it applies to all users of the Northampton’s public water supply. The restriction limits nonessential water use between 9 a.m. and 5 p.m.

Limiting water use is needed to ensure a sustainable water supply and to protect stream flow for aquatic life, according to the city’s Department of Public Works.

“It’s our most precious natural resource,” Department of Public Works director Donna LaScaleia said Monday.

The city’s water system is regulated through the Massachusetts Department of Environmental Protection.

“The terms and conditions of our permit are such that when the stream flow in the Mill River drops below 26.3 cubic feet per second for a three-day period, we have to institute a water restriction,” LaScaleia said. “There is no discretion.”

Water uses banned include washing of vehicles, other than by commercial car wash, and washing of exterior building surfaces, parking lots, driveways or sidewalks, except as needed to apply paint, preservatives, stucco, pavement or cement. Irrigation of lawns and watering of gardens, flowers and ornamental plants, except by means of a handheld hose, is also banned. Irrigation systems may be used between 5:01 p.m. and 8:59 a.m.

Over the last four years, including this year, water restrictions typically go into effect in Northampton in May and June, with some as early as May 1 in 2017 and others as late as June 20 in 2016.

Statewide, 87 water restrictions are currently in effect, said DEP spokesman Ed Coletta. Ware and Northampton are the only communities in Hampshire County with a water restriction right now, and the only other two communities in western Massachusetts asking its residents to restrict water usage are Orange, Athol and Shelburne Falls.

That’s up from 70 last Thursday, according to a state map showing current municipal water-use restrictions published by the MassDEP Bureau of Water Resources Water Management Program.

Compared to the same time in previous year, only 56 municipalities had enacted a water restriction in 2017, and in 2016, 99 municipalities had water restrictions in place, Coletta said.

“Water is a very important resource that needs to be protected, especially when we get into seasons like this when there is a difficulty with keeping the water resource protected,” Coletta said.

The state’s water-level monitoring season normally runs May 1 through Sep. 30. During that time, municipalities have the option of setting a date-certain water restriction — meaning the restriction goes in place on a certain date and is not dependent on water level — or a stream flow restriction like in Northampton.

About 60 percent of those communities that enact restrictions do it as of May 1 and the rest follow the stream flow gauge, Coletta said. In both cases, once a restriction is put in place it remains in place for the rest of the season, according to Coletta.

In Northampton, the water restriction can be lifted when the Mill River’s stream flow rises above 26.3 cubic feet per second for seven consecutive days, but LaScaleia said that typically doesn’t happen during the summer months.

“We ask that people act responsibility and it is our hope that we don’t have to enforce any of the city ordnances that would fine folks for non-compliance,” LaScaleia said. “I very much appreciate people calling the DPW and asking questions so that they can better understand what the water use restrictions is and how they can abide by it.”

Emily Cutts can be reached at ecutts@gazettenet.com.