They grabbed buckets and brooms as the flash flood happened at about 9.30pm, sweeping water away from homes and businesses on Keymer Road and Parklands Road.
They also directed traffic away from the water so vehicles would not create waves, allowing residents to sweep the flood into a nearby drain more easily.
West Sussex County Council now aims to improve drainage in the Keymer Road area.
Kelly Harding, 32, who owns Bella June Flowers on Keymer Road, said the area has had a flooding problem for a long time.
“There was a really bad flood in October last year, she said, adding that her shop floor was completely ruined and that it had to be ripped up and concreted again.
The rest of the shop had to be fully refurbished too, she said.
But Kelly, who has owned Bella June Flowers for three years, said the water damage was nowhere near as bad on Monday thanks to the quick thinking of nearby residents.
“Every time it floods on Parklands Road and Keymer road now all the residents come out ready,” she said.
Kelly said about 15 people will come out to unblock drains, push away water and put down sand bags.
“It’s quite a sight,” she said, adding that the helpers saved her shop and that only her doormat got wet this time.
“We have residents in their dressing gowns, barefoot, in pyjamas, with kids in tow just coming out to try to sweep all the water towards the drain,” Kelly said.
She added that she was very grateful to them for their help, saying that it is ‘heartwarming to know that they are there’.
Kelly said the area got roughly three centimetres of rain in 30 minutes, and that the fire brigade arrived within ten minutes to help them.
“I’ve not seen Hassocks flooded like that in a long time,” she said.
“October flooded badly just in this area but this week it flooded badly all over Hassocks.”
Kelly said she thinks the cause of the flooding is a blocked drain in Keymer Road and fears it might have become clogged with cement.
“The water pours in and out of one drain and the other drain can’t keep up,” said Kelly, adding that Hayley Elphick, the owner of the nearby REFLEX @42 hair salon now places sand bags down as soon as the rain starts.
“That drain just needs unblocking, it’s as simple as that,” she said.
Kelly said she and Hayley, 31, have let West Sussex County Council know about the flooding through LibDem councillor Kirsty Lord (Hassocks and Burgess Hill South) who is trying to get the problem fixed.
Hayley said she also thinks the drain is blocked with cement.
“When this last happened I was here until 1am with a group of people trying to get to the bottom of the drain that was blocked,” said Hayley.
“When we got to the bottom there was just so much scree everywhere, you could see the water wasn’t making it through.”
She does not believe the flooding is caused by an overflowing nearby stream either, saying that lots of work has been done on the stream to prevent this from happening.
Hayley said she was the first resident outside as the latest flash flood began and got the sand bags out within five minutes of the rain starting.
She said she then called the fire brigade and Kirsty Lord who arrived within a few minutes.
Several firefighters got out of the fire engine to help residents push water up the hill as a group and into a functioning drain, said Hayley.
“It was a massive team effort,” she said, thanking everyone who helped, including Hassocks residents, the fire brigade and Kirsty Lord for alerting the council to the problem.
“I think I have PTSD now when it rains,” said Hayley.
“The second it gets bad I put the sandbags out for me and Kelly because I can’t deal with it.”
Councillor Kirsty Lord said she arrived at Keymer Road to find ‘a whole army of residents with their brushes’.
“The water was so close to breaching the shops that if they hadn’t have been there the two properties would have been flooded,” she said.
“It’s entirely thanks to residents that it didn’t happen,” she added, saying that it was great to see their community spirit.”
Ms Lord said she raised the issue with West Sussex County Council after the flooding in October and said that WSCC carried out ‘extensive investigations’ earlier this year, clearing all the drains to assess where the problem was coming from. “Separately, working with the Parish Council and local groups, we have set up a Hassocks Flooding Working Group, which is looking at other interventions to manage flooding in Hassocks,” she added.
Ms Lord said the three main issues are: whether the drains are silted up and not flowing properly, whether the drains’ capacity is not enough, and whether the discharge of water into the stream is not possible if the stream level rises in heavy rain.
She added that she had asked WSCC to add the Parklands Road drains to the 12-monthly cycle instead of the usual four-yearly cycle for side roads, which has been granted.
After taking pictures of Keymer Road on Monday, Ms Lord said she shared the images with the Highways department and had ‘a very positive and immediate response’.
Drainage engineers spent several hours at the site on Thursday (July 1) where Ms Lord discussed the situation with them.
“We established that the drains were clear and not silted up again and found out more about how the drains work and discharge into the stream,” she said.
Ms Lord added that they will need to look at engineering solutions and look at whether techniques like further natural damming could ease the flow.
“There is not a quick solution but WSCC are responding well to the issues I am raising and I will be pushing them to move forward to finding a solution,” she said.
“While the rain on Monday was unprecedentedly heavy, the drainage system at Parklands Road struggles with much less rain too so this will be one of my top priorities with Highways over coming months.”
Ms Lord also said she is pushing for the County Council’s ‘long-delayed’ Surface Water Management Plan assessments for Hassocks to be carried out because this could unlock government funding for drainage improvements.
On Tuesday (July 6), a West Sussex County Council spokesperson said: “We have been working closely with Cllr Lord regarding the ongoing maintenance and longer-term drainage improvements in the Keymer Road area.
“Our Highways officers plan to meet with her in the coming weeks to discuss where we are in terms of future planned works, as there is an issue with the drainage outlet into the river in this location.
“We had a significant rainfall event overnight last Monday/Tuesday that resulted in far more rain failing than any conventional highway drainage would be designed to deal with.”