Two-year-olds Rhys and Shaun Scott were found in the garden tank at the rented house in Dalgety Bay on 12 March 2016.
They were taken by ambulance to Kirkcaldy’s Victoria hospital, where they were pronounced dead.
The house owner had run a business breeding carp at the property.
A Crown Office spokesman said: “Crown Counsel have concluded that there should be no criminal proceedings following the tragic deaths of Rhys and Shaun Scott at their home in Dalgety Bay in March 2016.
“After carefully considering the reports that were submitted to the procurator fiscal, Crown Counsel have also decided that there should be no fatal accident inquiry as the reasons for the tragedy were established during the course of the investigation.
“That investigation was carried out by Police Scotland, the Health and Safety Executive and Fife Council with oversight from the specialist Scottish Fatalities Investigation Unit of the Crown Office.
“The family of Rhys and Shaun have been informed.”
At the time of the boys’ deaths, their parents Mervyn Scott and Sarah Aitken issued a statement in which they said: “Both boys were long awaited little soldiers who were full of love, happiness, fun and cheek. Individually and together they have touched the lives of everyone they met. We along with our family and friends are devastated at such a tragic loss from such a ‘freak’ accident.
“They have been taken from us far too early and will be forever missed and loved.”