Complex sentence: In 1960 legislation was introduced to promote seawater flushing on a larger scale, followed by substantial investments in a separate network although the system was unpopular due to the need to build a separate plumbing network in each house.
Split into simpler sentences: In 1960 legislation was introduced to promote seawater flushing on a larger scale, followed by substantial investments in a separate network. However, the system was unpopular due to the need to build a separate plumbing network in each house.