Plants, just like all living things, require a certain amount of water to survive. If there is no water available they will quickly die, often in a matter of days. Plants in planters and pots are at most risk as they heat up and lose moisture quickly. All plants, regardless of their location, will not survive if they do not receive adequate amounts of water.
The main reason plants may not have water available is when Metro Vancouver bylaws prohibit the watering of gardens with a conventional spray type sprinkler system. Hand watering is permitted in stages 2 and 3, and that can make the difference between a healthy landscape and costly plant replacements.
In the summer, trees may need slow watering that can be provided safely and within the water restriction bylaws. In the heat of the summer even large trees can be saved with the use of watering bags that are filled two to three times a week.