Complex sentence: Legislation in the mid nineteenth century gradually improved the situation; the Metropolitan Commission of Sewers was formed, water filtration was made compulsory, and water intakes on the Thames were forced to be moved above the sewage outlets.
Split into simpler sentences: Legislation in the mid nineteenth century gradually improved the situation. The Metropolitan Commission of Sewers was formed, water filtration was made compulsory, and water intakes on the Thames were forced to be moved above the sewage outlets.