MEXICO CITY (Reuters) - An agreement aimed at ensuring more regular water from Mexico to the United States has been reached, both governments said on Saturday, following a long period of tension over a decades-old treaty.

A new measure of the International Boundary and Water Commission, which oversees the 1944 U.S.-Mexico water treaty, will provide Mexico with "tools and flexibility to deliver water earlier in the five-year cycle," a statement by the IBWC said.

The neighboring countries have tussled over the 1944 treaty, which was designed to allocate shared water resources. Mexico is required to send 1.75 million acre-feet of water from the Rio Grande to the United States over a five-year cycle, supplying farmers with critical irrigation.

The Latin American country, however, has not fully delivered recently amid some of the most severe drought-driven water shortages in nearly 30 years.

Mexico said in its own statement that the measure would provide greater reliability and predictability in water allocations to users in both countries, establish new working groups and improve water quality in the Rio Grande basin.

The new measure was the result of 18 months of negotiation, the IBWC said.

Mexico and the United States will establish working groups to "develop water conservation for the benefit of both countries," the IBWC said.

(Reporting by Cassandra Garrison; Editing by Mark Porter)