Water Oaks are considered short-lived in comparison to many yard tree selections. Some post storm surveys you can read online indicate they are more prone to blow-down than one would think. Keeping that in mind, distance from anything you happen to like should be pretty far, considering their mature size. 7 feet is too close for almost anything, I think.

(Just search 'Water Oak' or 'Water Oak Storm Damage' and read the editorial articles and (few) journal articles about them first.Many are related to coastal storms, but may apply to you, even if you don't live in hurricane prone area.)

Here is a link that might be useful: a PDF about coastal tree selection....

What's on the other side of that ten foot strip? Are you aware of how wide the spread of the canopy can grow? What is it about Quercus nigra that seems a good fit for this location?

I'd say that it's time to come up with plan B....an architectural solution.

Agree with rhizo.
Even if you planted one of the 'columnar' oak selections that are out there on the market now, 7 ft - or even 10 ft, if you could put them right on the property line - is too close to the house; yeah, they do grow fairly upright, but they do acquire some width over time.
I sure wouldn't put Q.nigra (or any other large mature-size tree) that close to my house.

I sure wouldn't put a water oak that close to my house. They're shallow rooted (blow over) and they rot very easily when damaged.

I'd recommend a larger type crepe myrtle like 'Natchez' or 'Muskogee'.

I appreciate the responses and I see the concerns. It sounded like most of the problem would be fall risk. To address that, I made the little sketch below that shows where I want to put the trees. They would be right at the property line which opposite my house has a steep dropoff away from my house.

Also, my house is probably 40 feet high at the peak on side. that should mean that most of the weight of the tree would be on the opposite side, much of it overhanging the big slope away from the house. Since the house is a good half as tall as the trees will ever get, the green in my photo should be scale to the most that ever might over hang my roof.

I can see that there would still be some risk, but wouldn't these things reduce the risk considerably? And since nobody addressed the root question, does that mean it would not be an issue?

So, how large would you expect this tree to get in five, ten, and twenty years? And are you aware that is is one of the most weak-wooded oaks around? It will drop branches and large limbs on a regular basis. You'll have to be pruning it away from the house on a regular basis.

An interesting experiment for you would be to do a quickie drawing TO SCALE. Use a circle the appropriate size of a young water oak...say half mature size: 30X25.

I would say that a tree that has the potential to get the size of a mature water oak could cause damage to the foundation if planted 7 feet from a building.