Osama Krayem, 23, doused the home-made TATP explosive that he had carried into Maalbeek metro station with water before trying to dispose of it in the lavatory of the apartment where the attackers were based, La Libre Belgique newspaper said.
It said investigators thought his claims were “credible” as TATP, the favoured choice of the Isis militant group as it can be made from readily available chemicals, is in crystal form and dissolves in water.
Belgian TV station RTBF carried a similar report.
Belgian prosecutors declined to confirm or deny the reports when contacted by AFP and Krayem's lawyers were unavailable for comment.
Krayem was arrested on April 8th and charged the next day with “terrorist murders” over last month's suicide blasts at Brussels airport and Maalbeek station in which 32 people were killed and more than 300 injured.
He has also reportedly been charged with links to November's Paris attacks which left 130 people dead. Both attacks have been claimed by Isis and appear linked to the same cell of attackers.
Belgian authorities suspect Krayem, a Swede of Syrian origin, of buying the bags used for the Brussels bombings.
He was filmed on CCTV with Maalbeek metro station bomber Khalid El Bakraoui minutes before the bomb went off.
Krayem's lawyer Vincent Lurquin has previously told reporters that his client had also planned to blow himself up but decided not to go ahead with it.
Three men detonated suicide bombs in Belgium's worst-ever terror attack: brothers Ibrahim and Khalid El Bakraoui and Najim Laachroui.
A fourth man, Mohamed Abrini, the so-called “man in the hat” who accompanied the two airport bombers but did not detonate his own device, was arrested in Brussels on April 8th. He has also been charged over the Paris attacks.
Initial investigations suggest that the Brussels attackers had planned to hit France, but with police on their trail, decided Belgium was an easier target.