I use a pump for two growbed, this is so far the easiest and cheapest way for me to do it. Photo below is my water feed. Pump rating roughly 2000 Litres/Hour approximately 500~600 GPH.
This arrangement make it very easy for me to clean the pump. Take it out do a quick cleaning and pop it back in.
That red ball valve is open to the maximum, it was there to restrict water flow. But its not needed, too lazy to change the PVC pipe. It works so why bother.
The top part is just a "Tee" splitting water into two. Its not a perfect split, occasionally one side get more that the other due to trapped air causing unbalance situation. It normally fix itself after few minutes, unless its slanting to one side then the problem will stay.
This is easy and one pump do 2 growbed.