The Ordnance Survey Field Name Book 1835  tells us:

In Abbeyland townland, near the town of Navan - a gentleman's house with a large orchard attached.
Blackwater House was built in the 18th century and is located on the Blackwater River beside Blackwater Mill. It was usually was associated with the person who owned the mill. At one stage it was owned and lived in by the Spicer Family before they moved to Belmont.
Today the house , like the mill, is empty and derelict and is pictured below.

blackwater house

Blackwater House (Photo - the Inventory of Architectural Heritage)