Dear Kimberly,
Many thanks for getting in touch – raw DNA extraction yields from DNeasy PowerWater can be fairly low. In our case, most outputs ranged at ~900 ng total. You can obviously play with the kits descriptions a bit, e.g. extending beat beating, using higher input water volumes, etc. But even a few ng (and low 230 purity) would yield you plenty of DNA to amplify 16S from and sequence these with MinION!
All the best,
Max