Estimates of how many houses are at risk vary between 400,000 and one million. The costs are also difficult to estimate - a renovation can cost between half and a million SEK per house, says Martine Coevert of Rotterdam municipality.

- Only here in Rotterdam do we expect 20,000 houses that will have problems within 10-15 years, says Martine Coevert.

"Couldn't have done it without a bank loan"

She herself has had problems with her house but is now employed by the municipality to advise others in the same seat. Outside a brick house with large cracks in the phase end and the walls, she meets Peyman Sadighi who is in the final stages of her repair.

When he bought the house ten years ago, he did not notice anything wrong, but in recent years the situation with the house plot has become acute. He shows us down in the basement where instead of rotten wooden piles he now has cement walls that support the house.

- In the past, there were wooden piles here that they removed. Only this job cost 90,000 euros, says Peyman Sadighi.

- I'm glad the bank was able to lend us money, otherwise we would not have been able to. With my salary, you can't pay for this, he says.

Leads on water from a canal

So the problem lies beneath the surface. As the groundwater has dropped, the piles supporting the house have started to rot. The periods of less rain, drought and low groundwater have become longer here, which speeds up the process. Last summer they were the driest in over 40 years.

On trial, the municipality of Rotterdam is now directing water from a channel below the ground surface towards houses affected by rotten house piles. The hope is to be able to raise the groundwater so much that the water protects the wooden piles even during the dry period. But those who can afford, or can get bank loans, have already started replacing the wooden piles with cement.

- I don't have a headache for long. I can live with peace now, says Peyman Sadighi.