The Reciprocity Treaty of 1875 removed tariffs on sugar exported to the United States. But to raise their production a steady supply of water was needed for the semi-arid dry forests of Pāʻia. Alexander realized that rain was plentiful miles away in the rainforests on the windward slopes of Haleakalā mountain. Alexander proposed a irrigation aqueduct that diverted water from that part of Haleakalā to their plantation. Alexander knew about irrigation systems used since ancient Hawaii while he was at Lahainaluna, but this was on a much larger scale. He negotiated a lease of water rights from King Kalākaua and raised financing from other partners. It was initially a 20-year lease for $100 per year. His brother James did a survey. Work started on the aqueduct in 1876 and was completed two years later in 1878 (at over three times the estimated cost), just before a deadline in the lease.