Complex sentence: By the 1820s the Tank Stream, Sydney's original water supply, had become little more than an open sewer, and the growing colony had become reliant on wells or water carted from the Lachlan Swamps (now Centennial Park).
Split into simpler sentences: By the 1820s, the Tank Stream, Sydney's original water supply, was in dire straits. It was little more than an open sewer and the growing colony was reliant on wells or water carted from the Lachlan Swamps (now Centennial Park).