Watering tomatoes while on Hols

I'm planning to go away for a week and have six tom plants in two growbags (at home).

I don't want to bother anyone with the task of watering them, so does anyone have any good ideas for an automatic (and cheap - perhaps self made) watering system?

Thanks Yorkie.

Yes, I do have a tap nearby, although I also have three large waterbutts nearby too and I'd hoped to not leave a tap turned on for a week (we're on a meter and a problem that resulted in the tap running for days would be expensive). Your suggestions looks good (and cheap) though.

Any other thoughts folks. I've read about fittings for upturned plastic bottles that drip feed the water - anyone tried those?

Yes, thought about that sort of thing too.

But electricity, water, outdoors, unattended for days .... hmmm.

It has worked for me for years.   Timer on a plug inside the shed, lead to the valve on the outside, valve all isolated.  No worries.      Cheers,   Tony.

use the Siphon principle, you can easily use a soft plastic straw to drip water to growing bag, run a test of how much water it drips, then use a paper clip on the straw to control the dripping speed, I did this to my peanut plant in house, effective

Thanks. I sense a project coming on.