The RAF has dropped a further 200 tonnes of aggregate on to a damaged dam at Whaley Bridge as residents are told they will not be allowed to return home until it is "absolutely safe".
An RAF Chinook from RAF Odiham spent more than eight hours shoring up the dam on Tuesday.
The RAF was called in last Friday and had already packed 530 tonnes onto the damaged part of the dam.
The Canal and River Trust said the water levels needed to fall by 8 metres and it has now dropped by 8.4 metres.
It means Toddbrook Reservoir is currently at just 25% of its holding capacity.
However, Derbyshire Police's Deputy Chief Constable Rachel Swann said evacuated residents will not be able to return to their homes until homes are "no longer at risk".
Around 100 military personnel in total have been drafted in to help with the dam, including more than 40 soldiers from the Light Dragoons.
The troops blocked a critical reservoir sluice gate with sandbags.
RAF Regional Liaison for the North West, Wing Commander Gary Lane, said: "The bags that we put in on Friday and Saturday have settled out a little bit, so we've got a bit of a concave area.
"The engineers wanted it a little bit smoother, so that's why we regenerated the aircraft, flew up this morning, and has now gone into the task to drop more bags, potentially up to 200 tonnes more aggregate to fill that void."
More than 1,500 people have been evacuated from Whaley Bridge since last Thursday following heavy rain.
However, a small number refused to leave their homes despite fears the 300-million-gallon reservoir could flood the town.
Derbyshire's Police and Crime Commissioner, Hardyal Dhindsa, told residents he recognised the "disruption" but added the priority was still a "threat to life".
"We do not want anyone to be devastated. We want to make sure we protect the properties of everybody. That is going to be difficult when there is an evacuation," he said.
Fire crews have also been helping to shore up the dam, using 23 high-volume pumps to remove the reservoir's water into the River Goyt.