What characteristic must non-potable water meet for use in concrete?

Non-potable water used in concrete must be free from contaminants to ensure the integrity and strength of the concrete mix. Water that contains harmful substances, such as oils, acids, or organic materials, can negatively affect the hydration process of cement, leading to potential weakness in the final concrete product. Additionally, contaminants can lead to issues like corrosion of reinforcement steel or staining of the concrete surface. Therefore, while non-potable water can be used for concrete applications, it is crucial that it is clean enough to not compromise the desired physical and chemical properties of the concrete.

The other options provide characteristics that do not align with the necessary conditions for non-potable water use in concrete. Hot water is not required; in fact, temperature management can often be critical during concrete mixing and curing. Additives may enhance certain properties of concrete but are not a prerequisite for using non-potable water. Recycling of water is a common practice in concrete production, provided the recycled water meets cleanliness standards.