This paper reports on a low-cost turbidity sensor design for continuous on-line water quality monitoring applications. The measurement of turbidity by agricultural and environmental scientists is restricted by the current cost and functionality of available commercial instruments. Although there are a number of low-cost turbidity sensors exploited within domestic 'white-goods', such as dishwashers, the lack of sensitivity and power-usage of these devices make them unsuitable for freshwater quality monitoring purposes. The recent introduction of wireless protocols and hardware, associated with the 'Internet-of-Things' concept for machine-tomachine autonomous sensing and control, has enabled the largescale networked intelligent water turbidity monitoring system that implements relatively low-cost sensors to be developed. The proposed sensor uses both transmitted light and orthogonal (90 degrees) scattered light detection principles, and is 2-3 orders of magnitude lower in cost as compared to the existing commercial turbidity sensors. With an 850nm infrared LED, and dual orthogonal photodetectors, the proposed design is capable of measuring turbidity within the range of 0-1000 Nephelometric Turbidity Unit (NTU) with improved accuracy and robustness as compared to the existing low cost turbidity sensors. The combination of orthogonal and transmitted light detection unit provide both 0-200 NTU high resolution and accuracy sensing and 0-1000 NTU lower resolution and accuracy sensing capability. Results from calibration experiment are presented, which proved that the proposed sensor design produced a comparable turbidity reading as a commercial turbidity sensor.