Wilted plant leaves are a sure sign of a watering issue. Have no fear! If you catch this in time, they should all bounce back to 100% as soon as they get water again and the effects will soon reverse and go back to normal.
The first thing to check is that there is water in the reservoir. If the water level is below the top of the pump it will no longer circulate and the plants will eventually wilt and then die. To fix this, simply top up the reservoir! while you're at it, you can also clean out the reservoir and add nutrients since the water level is already low.
The next issue could be a defective pump. The first cause of this issue is letting the pump run with low or no water. If the pump is the culprit you may notice the following:
1) pump running but no water is flowing
2) pump is running but very little water is flowing
3) pump is not running at all while plugged in
in order to fix this issue, please visit the article on pump troubleshooting to follow the steps to fix this.