Various raspberry pi-based watering systems.
Version 1.0 was designed to be used inside, to water a few plants while I am away. It uses two 3-6V submersible pumps, controlled from a raspberry pi via a relay, to pump water through some tubing onto some potplants.
Version 2.0 was designed to be used on a balcony (with no mains water tap but with power points), again to water a few plants while I am away. It uses a slightly more powerful (mains-electricty powered) pump, controlled via a radio-frequency power socket, to pump water onto some plants. It incorporated a sensor to warn of a nearly empty water reservoir.