McALLEN, Texas (Border Report) — Last week’s tropical storm and depression brought much-needed rain to deep South Texas and slightly boosted two critical international reservoirs that supply water to the border region.

But it did not deliver the expected deluge far enough to the northwest where it could have sent water surging into Mexican tributaries that feed the Rio Grande.

“While the recent rains we have received were beneficial, the rain did not fall in the reservoir watershed which is essential to replenish this water supply,” McAllen Public Utility General Manager Mark Vega said Tuesday.

Falcon Dam, in Starr County, was at 12.5% capacity on Tuesday, according to the latest data from the Texas Water Development Board. That’s up from a record low of 9.5% on May 25, and is a direct result of rains that came in when Tropical Storm Alberto, which made landfall in Mexico on June 20.

Amistad Reservoir, outside Del Rio, Texas, was at 24.5% on Tuesday, the state water agency reports.

Both reservoirs still are considered critically low and experts warn that it will take a lot more rain to buoy water supplies in the absence of Mexico paying the water that it owes to the United States and the Rio Grande during this current five-year cycle.

Under a 1944 international water treaty, Mexico is required to pay the United States 1.2 million acre-feet of water ever five years. Although the current cycle ends in October 2025, Mexico so far has only paid just under 400,000 acre-feet of water, only about one year’s worth, according to data from the U.S. Section of the International Boundary and Water Commission.

Earlier this year, the state’s only sugar mill in Santa Rosa, Texas, shut down because there’s not enough water for farmers to grow the thirsty crop, and Hidalgo County remains in a drought disaster declaration.

But the rains did bring relief to the remote ranching community of Zapata, Texas, which had been just inches from not being able to extract water from the shrinking Rio Grande.

“The rain really helped out,” Ralph Treviño, water district manager for Zapata, told Border Report on Wednesday.

Almost 2 inches — 1.89 inches — fell in Zapata from June 18 -20, and Treviño said more rain hit upstream in San Ygnacio.

Altogether, Zapata got about 3 inches of rain from the tropical storm and lingering after effects, according to data from the National Weather Service.

“It’s been good news,” Treviño said. “The waters reached all the way to Eagle Pass and Laredo and are making its way down.”

Zapata gets its drinking water from the Rio Grande right before it drains into Falcon International Reservoir, commonly known as Falcon Lake. The water district’s main intake pump is under a shed at the end of a catwalk on the Rio Grande.

Levels at the intake pump went from 251.5 feet before the storm hit to 254.8 feet on Wednesday, Treviño said.

The town was at risk of not being able to extract water from the Rio Grande if levels fell below 247 feet.

He said the rain also filled water holding reservoirs throughout the Rio Grande Valley, reducing the demand for water to be released from the international river and allowing the two main reservoirs to hold and boost capacity.

Zapata, however, remained at Stage 3 water conservation restrictions. But for the time being, is not at threat of moving to Stage 4.

McAllen, about 100 miles downstream, remains at Stage 2 water restrictions after receiving a record 4.29 inches of rain associated with the tropical storm. That means residents and businesses can only water twice a week and only on certain days depending upon where they live.

“It is important that as residents of the community, we follow the mandatory water restrictions out of necessity to ensure a continued adequate water supply and pressure for the coming months,” Vega said.

Sandra Sanchez can be reached at SSanchez@BorderReport.com.