Atomstroiexport experts are working on the $1-billion plant in Bushehr, 400 kilometers (250 miles) southwest of Tehran on the coast, which was previously scheduled to become operational by the end of 2006 but that date has been set back to the second half of 2007.
"These are auxiliary facilities at the NPP and their launch allows us to start testing the main systems and units," the company said in a statement.
The deionized water produced by water processing will be used to flush pipes and other parts of a power unit at the NPP.
Iran has been at the center of an international dispute this year over its nuclear ambitions. Some countries suspect the Islamic Republic of pursuing a covert weapons program, but Tehran has consistently denied the claims and says its needs atomic power for civilian needs.
The company is Russia's leading organization implementing intergovernmental agreements on the construction of nuclear facilities abroad. The company is currently building five power plants in China, India and Iran.