When taking a sprinkler system out of service, which of the following is an approved source of a temporary water supply?

Using a hose from a fire hydrant as a temporary water supply is appropriate because fire hydrants are designed to provide a sufficient flow of water under pressure to assist in firefighting and emergency response efforts. This method ensures that there is an adequate supply of water to maintain the sprinkler system's functionality while it is out of service.

A fire hydrant can deliver a significantly higher volume of water compared to other options, making it suitable in scenarios where a sprinkler system needs to be temporarily supplemented for maintenance or repair purposes. It is critical that the connection to a fire hydrant is performed in accordance with local regulations and guidelines, ensuring that it does not jeopardize the public water supply's integrity.

In contrast, using a bucket of water or a garden hose connected to a building faucet would not provide the necessary volume or pressure required by a sprinkler system, leading to ineffective operation and increased risk during the out-of-service period. Therefore, relying on a fire hydrant is the only viable and approved method among the options listed to maintain operational readiness of fire protection systems during maintenance activities.