What is the most important building in London's history? St Paul's Cathedral? Westminster Abbey? The Tower of London? My vote goes to a grand 19th Century building in the marshes on the edge of Zone 3, set between a non-league football club and the muddy banks of the River Thames.
While Crossness Pumping Station may not feature on a postcard, it has perhaps played a bigger part in changing the lives of ordinary Londoners than any other building, saving thousands from death and disease.
I have to admit I'm a bit biased. My great-great-great grandfather Sir Joseph Bazalgette designed and built Crossness, which celebrated its 150th anniversary on 3 April. Stepping inside, it looks more like a palace than a sewage treatment works, with imposing red pillars and ornate iron lattice detail in green and gold. But this was a building with a purpose: setting out to save a city drowning in its own waste, at a time when Londoners were quite literally seeing sewage coming up through their floorboards.
Punch Magazine, 1883
Let me take you back to London before 1865. The industrial revolution had swept through Britain, the urban population had swollen and people were living in overcrowded, unsanitary slums. Cholera and dysentery plagued the city. This was the place Dickens and Mayhew wrote about in their novels: the infernal stink of the River Thames and the fetid streets where no clean water flowed. Life expectancy was less than 20 years for people in some towns and cities - and my great-great-great grandfather lost four of his siblings before they reached their second birthdays.
One mother, Christine was recorded as having lost her young son Stephen to cholera. "The drains get flooded, the toilets get flooded - everything floods," said Christine. "The children get diseases. They get sick. When Stephen got sick he started having diarrhoea and became very dehydrated. I can't forget my son, I always remember him and I feel the pain of losing him all the time. I fear that my other children will suffer from diarrhoea. We have been advised to boil our water, to give them hot food, but I still worry. Most people here don't have toilets... so we use bags which we then dump."
But this is all ancient history, right?
Well actually no. Christine and Stephen didn't live in 19th Century London - Christine lives today in 21st Century Kampala in Uganda. But the conditions she faces are much the same as Dickens would have recognised: a densely populated slum with no access to clean water, no toilets, a world where rampant disease is inescapable.
But it doesn't have to be like this. Soon after opening, Crossness helped transform London: an innovative system of 1100 miles of flowing water in underground tunnels, taking away 31 billion gallons of sewage per year - flushing cholera and dysentery off the streets of London town. This may seem common sense now, but at the time it was revolutionary thinking. After placing an advert in the Times, Bazalgette received over 137 different madcap ideas. One contemporary, WH Smith of stationery fame, even suggested running trains out of London carrying human waste!
But it wasn't just plucky old fashioned Victorian engineering that changed London's sanitation fortunes: Bazalgette campaigned tirelessly for sanitation reform in the Houses of Parliament: it was political will as much as clever design that brought the issue under control.
It means there can be hope in a place like Uganda today: that through political action and urban planning, we can change the fortunes of people who live in dangerously unsanitary conditions. Over 748million people around the world still don't have access to clean water, while a massive 2.5billion people do not have access to a toilet.
International charity WaterAid has launched The Big History Project - calling on people to uncover the history of taps and toilets in their own local area, to show how change is possible. This year is an important year for international development with the setting of the Sustainable Development Goals, new global UN targets to end extreme poverty. Dedicated water and sanitation goals are vital to improve not only health, but education, gender equality and economic growth.
Let's make 2015 the year we decide to resign to the history books, unsanitary living conditions like Christine's, where they belong.
The opening of Crossness Pump Station made the front page of The Illustrated London News, 1865 (c) Westminster Archives