Final answer:
Rainwater harvesting is the most cost-effective water-collection system among the options.
Step-by-step explanation:
Among the given options, rainwater harvesting is the most cost-effective water-collection system. Rainwater harvesting involves catching and storing rainwater for reuse before it reaches the ground. It is a sustainable and affordable method that can be implemented by individuals and communities to meet their water needs. On the other hand, iceberg harvesting, desalination, and cloud seeding are generally complex and expensive processes that may not be as efficient or economical.