I think you have received some bad information on how oxygen based intestinal cleansers work. They actually convert your compacted fecal matter from a solid form into a liquid or gas. This means there is very little risk of dehydration. Yes, you are correct that you still need to consume at least half of your body weight in ounces of water. The reason for this to help flush the toxins out of your body more quickly. I am not sure why your Vitamin D levels, however, I did notice when you are actually taking your multi-vitamin and the Mag 07. If you are taking them at the same time, this might explain why your body is not absorbing the Vitamin D. Another thing you might consider is the quality of the multi-vitmain as well as the extra vitamins that you are taking. I personally take Oxypowder at night and my other supplements in the morning with the exception of my calcium supplement. I take it at 6:oo p.m. I then take my Oxypowder at around 10:30 p.m. This allows my body to absorb the calcium. You should always take any oxygen based intestinal cleansers at 4-6 hours apart.If you have more questions about oxygen based intestinal cleansers, you can visit http://www.colon-cleanse-constipation.com/
I hope this helps you and I want to wish very good health.