27h. May 1807.
Agreeably to your request of the 25h. I have ascertained the height of the water in the branch and Spring, where Massachusetts Avenue crosses 16th Street west; the former is 9 feet 9 inches, and the latter 8 feet 6 inches above the base of the presidents house. The highest part of the ditch in 16th. Street is about 8 feet above the base of the house; at the intersection of K Street and 16h. Street the ground is one foot, and at the crossing of L Street 2 feet 8 inches lower than that point.
If it is desirable to bring the water of the branch and Spring to the presidents house along 16th Street, it must come in pipes, as some of the ground is more than ten feet below the head of water, and also considerably lower than the place where it will be discharged. Should carrying the water along the surface in an open canal be preferred until it arrive at the ridge where the cut is now made it will have to be taken so far to the eastward as to cross K Street near Vermont avenue, intersecting the lots and Streets in its course.
The surface of the garden, at the gate, is two inches longer than the base, or freestone work, of the house.
The distance from the Presidents house to the Spring is about three thousand Six hundred feet along 16h. Street.
With great respect I am Yours Truly
DLC: Papers of Thomas Jefferson.