Complex sentence: Near the North Tower, there was another constructed tower, however, it is not part of the Lavra fortification because it housed a water tower, designed by the architect V. Sychugov and constructed for the Lavra's fresh water supply in 1879.
Split into simpler sentences: Near the North Tower, there is a water tower, which is not part of the Lavra fortification system. It was designed by the architect V. Sychugov and constructed to ensure the Lavra's fresh water supply in 1879.