DIY Top off system???

[Aquattro]

I use a 5g water jug from Save-On Foods hooked up to a Kent float valve. Been using this setup for a year with no problems. The lid of the jug allows for a 1/4" mnpt compression or John Guest fitting. Jug was $9 full of RO water and the float valve was from J&L, don't remember the cost.
HTH