@Mirna65 Yes, the host should really mention this in the listing. You don't say how long your stay was, but if it was several weeks or more, many hosts discount longer term bookings, and provide "starters" for guests, like a few bottles of water, enough toilet paper for the first few days, etc, and guests are expected to provide for themselves after that.
Did the host offer any explanation for why the water is brown, or did you ask? There maybe nothing at all unsafe about it, it might just have a high iron or other harmless mineral content. So while it might not taste that great, and be visually unappealing, it might not actually be dangerous to drink. If that's the case, then maybe the host didn't think it necessary to mention in the ad. If she's a newish host, it's often hard to anticipate what might bother guests, especially if it's something the host is used to and doesn't consider any big deal, and to then make sure to include the info in the listing info.
I would suggest that you send her a private message saying that she should include the water info in her listing ad.