Environment Minister Ross Finnie is expected to come under pressure from MSPs to explain the sudden resignation of Scottish Water's chairman.
Opposition parties want to know what Professor Alan Alexander's departure means for the Ј2bn programme of investment in water supplies.
They suspect he resigned because he believed the funds available were not enough for the necessary improvements.
Mr Finnie said he was relying on advice from the new water commission.
The Scottish Executive has provided Ј2.1bn to improve Scotland's water supplies and sewage system over the next four years.
Scottish National Party environment spokesman Rob Gibson, who will lead Thursday's debate in parliament, said Scottish Water was being asked to deliver better water and pollution standards and connections to new housing developments without the necessary funds.
"In the run-up to Prof Alexander's resignation last month, ministers repeatedly told us that the infrastructure programme was on target and there were no problems.
"In light of recent events, that is evidently not the case.
'Hollow assurances'
"This has left customers and developers staring into an abyss."
He said "swift and effective" delivery of upgrades to the water network was vital to customers, local communities and the development of the Scottish economy.
"Ministers have managed to sleepwalk their way into this crisis with their hollow assurances that everything at Scottish Water is on track when they are clearly not," he said.
"Much as they may like to claim otherwise, the buck stops with the Labour and Lib Dem ministers responsible for Scottish Water.
"They must take the opportunity of today's debate to clearly set out what steps they are going to take to get Scottish Water's plans back on track."
(BBC)
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