Galena
Landlord.
My flask is 2 litres so I can only make 1 litre starters. But my thinking was I could split it and save half and make a fresh starter with the other half to use on current brew.
If you can make 1.5 litres with it then yes, you would need 1.5litres water to 150grams DME and then you would use 1 litre and save 0.5 litre
I tried with the yeast starter calculator and it does not seem that it can be done with 1 litre.
However you could make it in a sanitised plastic bottle and shake it well and regularly