Critical infrastructures across many industries such as smart water treatment and distribution networks (SWTDN) and power generation and public transport networks depend on the supervisory control and data acquisition (SCADA) system. However, being the core component of the critical infrastructures has made the SCADA-based SWTDN system an attractive target for cyberattacks. A successful attack on the SCADA will have a devastating impact on an SWTDN in terms of proper operations; therefore, safeguarding the SCADA from cyberattacks is paramount. With the increasing cyberattacks on SWTDN, both in number and sophistication, the need to detect these attacks early has become a subject of great interest among practitioners and researchers. To this end, we propose a novel strategy, based on a semi-supervised approach. Two semi-supervised approaches, including unsupervised learning and deep learning-based approaches, have been proposed. The proposed approaches can involve learning dynamic cyberattack patterns from unlabeled data in an SWTDN. We validate the proposed semi-supervised approach experimentally using an operational water treatment plant testbed. The proposed approach achieved almost 100% accuracy and substantially outperforms the existing baseline approaches used in this paper. The outcome of the experiment is encouraging and demonstrates the potential use of the semi-supervised approach for security control in smart water distribution.