I found this article for a “A Regeneration Strategy For Valletta” which is a case study made by ENTRUST, a research project supported by the European Commission.
It talks about the different issues of Valletta, such as demographical issues, economic and social issues, tourism, physical aspects and infrastructure. It mentions also reasons for degradation of buildings such as pollution, traffic etc.
Another interesting text about Subterranean Valletta, its water reservoirs, cisterns and tunnels can be read here.
If you find similar texts about these environmental/occupation issues and about the water collection system, I would be grateful if you could share them here/ with me 😉