The use of seawater and sea-sand in producing concrete has attracted increasing research attention in recent years to address the shortage of river sand and in certain applications the shortage of freshwater. In particular, reinforced concrete structures made of seawater sea-sand concrete (SSC) and corrosion-resistant fiber-reinforced polymer (FRP) are particularly attractive for the development of coastal and marine infrastructure (e.g. on remote islands) as durable structures can be created using locally available materials. Existing studies on SSC or seawater concrete have been largely limited to the use of mixing water with a salinity level close to the world-average ocean salinity. Against this background, the present paper reports the first ever systematic study on the effect of salinity of mixing water on the properties of concrete. The present study covered a wide range of salinity levels from 16.5 g/L to 82.5 g/L, and examined a wide range of short-term concrete properties including the heat of hydration, shrinkage, compressive strength and modulus of elasticity. The test results show that the salinity of mixing water has a considerable effect on the rate of hydration heat and shrinkage at early ages, as well as the cumulative release of hydration heat. It is also shown that the water salinity has a slight negative effect on the compressive strength and modulus of elasticity of concrete at ages older than 14 days.