Many Bangkokians were left frustrated in heavy traffic congestion following the downpour which placed several low-lying areas under water.
"I don't want to criticise City Hall," said Royol Chitradol, flood monitoring panel chairman under the state-appointed Water and Flood Management Commission. "But we have told it [to improve the flood drainage facilities]. It did nothing, claiming the job in some areas belonged to the Highways Department."
Mr Royol said drainage flaws could be found in sewers which were too small in front of the Army Club on Vibhavadi Rangsit Road and clogged drains at Sutthisan intersection which were hit hardest following Tuesday's rain.
The Bangkok Metropolitan Administration (BMA) had boasted about giant underground tunnels it had built as storm drains, but water hardly flowed into them because the capital's landscape was mostly flat, he said.
He suggested City Hall use water-pushing machines in canals to help speed up drainage.
Prime Minister Yingluck Shinawatra said the slow drainage might be caused by problems including garbage in sewers, clogged canals and the possibility that the underground tunnels might not work to their full capacity.
"We don't know their actual capacities because sometimes floodwater may not flow [into the tunnels]," she said.
Bangkok has seven drainage tunnels with diameters ranging from more than 3 metres to over 5m. The tunnels, built as the "expressway" for floodwaters in major city venues, were designed to drain 155.5 cubic metres of water per second.
Bangkok deputy governor Wallop Suwandee said up to 29 areas in the capital were flooded on Tuesday.
He argued, however, that most of the water had been drained from the roads in a few hours. But city officials admitted that there were still some flaws in Bangkok's drainage system.
They said although the water had been drained from city canals earlier to make room for floodwater, the heavy rainfall rapidly filled them, hampering the drainage of water.
They also said heavy rain now posed more of a flood threat to the city than run-off from the North.
This month's rainfall has been measured at 800 millimetres, half of which took place over the past four days, deputy Bangkok governor Teerachon Manomaiphibul said.
"The rain volume is now more than 100mm every day," he said.
Meanwhile, National Disaster Warning Centre director Somsak Khaosuwan predicted yesterday people in Bangkok and nearby provinces could expect more rain until Saturday.
Although the rain has brought only brief flooding to Bangkok, many people have begun to question the authorities' ability to cope with a potential flood disaster this year.
Prime Minister Yingluck defended the government over its role in handling the flood situation in Bangkok.
She said the government has worked with City Hall in trying to prevent more flooding but it could not force it to follow its orders.
"This is our limitation," she said. "We cannot do the job ourselves without the city officials."
To help improve the drainage in Bangkok, the prime minister said she had ordered the Corrections Department to mobilise prisoners to clear clogged sewers.
Department chief Suchart Wong-anantchai said he is preparing to recruit 2,000 inmates, with good behaviour, to carry out the cleaning.
Meanwhile, the Rajaprajanugroh Foundation under the patronage of His Majesty the King yesterday gave flood relief supplies to 1,000 villagers in Phitsanulok's Bang Rakam district, where run-off from Sukhothai has damaged more than 50,000 rai of rice fields.
HRH Maha Chakri Sirindhorn has also sent boats and survival kits to flood victims in Ayutthaya's Bang Ban district, which has been declared a disaster zone.
In another development, Pheu Thai MPs will today meet Bangkok Governor MR Sukhumbhand Paribatra to discuss the city's alleged delay in handing flood compensation to Don Muang residents.
The residents blocked a section of Vibhavadi Rangsit Road on Tuesday to demand City Hall pay 20,000 baht in compensation to each affected family.