They require a constant source of cool, clean water.

The iron oxide process requires an efficient source of heat.

Such an increase requires an external source of energy.

Human studies required a better source of the radioactive Iodine.

They do not generally require a source of water other than food, but will use it given the opportunity.

Power required a source, and someone to control it.

To bring over any substantial numbers in the future would certainly require a source of grant funding.

For its missiles to be effective, China would require a source of data about possible targets.

Guided missiles require a source of electrical power during flight.

However, this requires a bright and highly monochromatic light source to be effective.