Do you have to drain all the sugar water from water kefir regularly? I know that water-kefir grains need to be fed sugar and minerals every 24 to 48 hours, but my question is whether I can withdraw just 25% to 50% of the sugar water, and leave the rest of the sugar water as a sort of "starter" to speed up the next fermentation, and add enough sugar and dried fruits or sea salt for the total amount of liquid being fermented or according to taste or need?

Meaning, is there a problem with leaving a lot of old sugar water regularly and just adding sugar and minerals with minimal water every 24 to 48 hours?

Please note that I'm not asking about taste or for any subjective advice; I'm asking whether old sugar water creates any problems for the kefir grains, from lingering yeast or anything like that, or compromises the grains' health or activity in any other way.

Thank you.
Technically, you can. 

The advantage of cleaning is that you can start with the right amounts of kefir, water, sugar and whatever you add. If you are aiming for a certain taste, starting from scratch makes it easier to match again.

If you don't, there won't be a problem (at first), but as time goes by the chances of contaminations in the residual water will grow. Those contaminations can affect the grains.