The amount of fertilizer in the soil will influence the reading. If you fertilize heavily, the meters tend to read that the soil is moist even when the soil is dry. Water should be at room temperature. This is especially true for tropical plants. The best time to water is in the morning.
Tap water is acceptable for watering most plants.
Some plants are susceptible to fluoride injury from treated water. Fluoridated water should be allowed to sit at room temperature over night before using. Softened water should not be used since it contains sodium, which can increase the soluble salt levels in the soil.