In an Alternate Earth timeline, round about 1200 AD, we have the Great Alchemist and Philosopher Bob. Bob, being from a wealthy family has a handful of older brothers, so he's not likely to be an heir. He was raised with a rather eclectic variety of tutors and he did have an indulgent father, so when he came of age, he was allowed to travel extensively.
Bob is unusually open minded and curious, so during his travels he noticed something. Cultures that were more fastidious about hygiene tended to have people who lived longer (as long as they didn't die violently, or from starvation). He also noticed that places that had lots of fast moving water and few swamps also tended to have more people living to old age. He also found that deep wells in mountainous regions had much better tasting water.
Bob has the gift of original thought and comes to the conclusion that cleanliness is a key to longer life. He gets home and demonstrates to his father that water from a fast moving river tastes better and that a good bath feels good. He also shows his mother that the forest smells better than town, and asks if she would be happier if he could help the town smell better.
Bob embarks on a series of public works, funded by his father and enlisting a great number of craftsmen and nearby alchemists. He wants to:
- scale up a number of alchemical tools to purify and distill water
- build a centrally located system of water storage
- find ways to remove waste from the city
- improve agricultural output
Bob also figures that things that keep people healthy will keep livestock healthy. This is in addition to any sort of plant based agricultural improvements.
So I ask you, how far can Bob get in his lifetime (he's about 27 when he gets back from his travels)? Assuming he's going to live the proverbial 4 score and ten years (70) and he will be resetting the city up to and including demolishing areas of the city as he needs to. Only the main castle needs to remain, but with improvements. The city wall needs to be maintained, but can be altered to fit whatever.
The only real limitation is that methodologies be related to making things cleaner (filtration etc.), healthier, and known somewhere in Europe and Asia by around 1200 AD.
Assume Bob's dad is extremely wealthy, so money is no problem. Bob can also enlist at least one master craftsman from just about any discipline. It's a peaceful time in the region. The city itself is landlocked, near a fairly swift but navigable river, and is pretty sizable for anything other than a major port or capital city.
The goal is to get to industrial revolution within 4 generations. Is this enough?
I'll be happy to add details for specificity or to refine restrictions as necessary.
Quick Edit: It's understood that Sanitation alone isn't going to turn the trick. I'm looking at the increased lifespan and increased agricultural output being the foundation when combined with the increase in knowledge from multiple disciplines working together.
Edit 2: Perhaps this is more about finding underpinnings of technological advancement that are not directly related to massive armed conflict. To work through rough logic: better sanitation means reduced disease. More agriculture output means more base wealth. These both mean longer lifespans. Master craftsmen being encouraged to work together should mean increased and more broadly distributed knowledge and as a side effect, creative thought goes up.