1. Observe the transparent bottle body: if the bottle for water replenishing spray is transparent or translucent, you can directly observe the remaining water volume through the bottle body. Place the bottle in a well lit area, tilt the bottle, and estimate the remaining amount by looking at the side or bottom of the bottle.
2. Weighing comparison: If the bottle is opaque, the weighing method can be used. Weigh and record the weight when the spray bottle is full. As used, weigh again regularly and estimate the remaining amount by comparing the weight difference between the two measurements. Note that this method needs to ensure that there are no other objects attached or left when weighing the spray bottle.
3. Mark the scale: if the above methods are not applicable, you can mark the scale on the spray bottle by yourself. Use a marker or sticker to mark the water level line on the bottle in a certain proportion. After each use, estimate the remaining amount based on the position where the water level drops. This method requires a certain level of estimation and labeling skills, but once completed, it is easy to check the remaining quantity at any time.