Water timer for RO system

I am looking for some sort of timer to water my plants while I am out of town for up to a week. I have a 5 stage reverse osmosis system that I want to use. Currently I just get the RO water from an extra faucet next to my sink. What I want to do is tap off of that and run a line to the bathroom where I will have my plants in the bathtub. I already have plenty of tubing and spray nozzles, but now I just need some sort of timer that will open a valve on the RO line. BTW, this is a soil grow. Just 3 plants.

i would suggest getting a resevoir to keep your clean and ready with a pump and have the pump on a timer and time depends on what medium you will use