I'm considering some land in Cowlitz County WA for off-grid homesteading. Has anyone had experience with the water/mineral rights, etc for this county? Any other considerations for this county?

I live in Cowlitz County, but I don't have much experience dealing with the county government. I've heard mixed reviews from others, but they were mostly building contractors dealing with code inspectors. my general impression is that it would be relatively easy to fly under the radar, so to speak, but don't take my word for it.

NOT SPECIFIC TO COWLITZ COUNTY:
Mineral and water rights will vary.

Normally, mineral rights come with the property, unless a previous owner has sold them.
The deed should specify if the rights belong to the property, or somebody else.

Water rights are entirely different. You are entitled to use whatever is available for household use. For agricultural use, you need Water Rights. They do not automatically come with the land. If the current owner has water rights, he may, or may not include them with the property. He may sell them apart from the property (even to somebody else).

Even if you pay $20,000 to have a well put in, unless you specifically have water rights, you may only draw enough water from that well for household use. Household use can include a 'normal garden', but not a dozen or so fruit trees, or a half acre of corn. Most areas have daily limits on how much you may use for 'landscaping'.

WA is not as militant about water rights as some other states are (CO, OR, UT). West of the Cascades, nobody seems to even think about it, but as you move further into the rain shadow, water rights are on everybody's mind. I have heard of cases where one neighbor would turn in another if they thought the lawn looked too green in late summer.