Roof tap rainwater harvesting system in Rajasthan is known as 'Tanks'.

Explanation:
- Rainwater harvesting is the process of collecting, storing, and using rainwater for various purposes. It is an important practice in regions with limited water resources, such as Rajasthan.
- In Rajasthan, a common method of rainwater harvesting is through the use of tanks.
- Tanks are structures that are built to collect rainwater from rooftops. They are typically made of concrete or other materials and are designed to store large amounts of water.
- The roof tap rainwater harvesting system involves the installation of a network of pipes and gutters on rooftops. These pipes and gutters collect rainwater and channel it into the tanks.
- The collected rainwater can be used for various purposes such as drinking, irrigation, and domestic use. It helps in reducing the dependence on groundwater and provides a sustainable source of water.
- The tanks used for rainwater harvesting in Rajasthan are designed to be large enough to store water for an extended period, especially during the dry season when rainfall is scarce.
- These tanks are often constructed in rural areas where there is limited access to water supply. They play a crucial role in ensuring water availability for both human and agricultural needs.
- The rainwater collected in the tanks can be used directly or can be treated to improve its quality before use.
- The roof tap rainwater harvesting system has gained popularity in Rajasthan due to its effectiveness in conserving water and providing a reliable source of water in arid regions.
- By implementing rainwater harvesting systems like tanks, Rajasthan can mitigate water scarcity issues and promote sustainable water management practices.

In conclusion, the roof tap rainwater harvesting system in Rajasthan is known as 'Tanks'. These tanks are designed to collect and store rainwater from rooftops, providing a sustainable source of water for various purposes.