I found Old Growth Cellar rainwater catchment through a facebook posting.
For what it is worth, I would like to report my own experience with a rainwater catchment on a house I own on Terceira island (Portuguese, situated on the mid Atlantic ridge).
Historically, many of the houses there had a rainwater catchment "cisterna".
In rebuilding the house which I bought in ruins, I thought it a good idea to incorporate a rainwater catchment for emergency use. There was no impelling reason for it, the area is served by city water. The catchment basin is rectangular, incorporated in the building under the terrace and holds some 400 cubic feet of water. Internal dimensions approx. 10' by 20' and 8' high. Max. water level about 7 foot. The water comes in through a drain pipe from part of the roof of the house.
The building material: hollow cement blocks, reinforced with steel and concrete pillars at the four corners, and at the midpoints of the longer side. Covered by cement ceiling, with a 1 1/2 foot square concrete lid for inspection and access to clean. Water can be drawn out either manually through a faucet set about half a meter above the bottom level of the construction, or by an electric pump with a bladder-type water pressure tank. This hooks into the house water piping. City water can be excluded when rain water is used.
I clean the tank every two or three years. Water keeps clear and odorless as it is in a (relatively) dark and cool storage place. The tank is completely covered by rock/earth only on one side. On two sides, the tank's cement stone wall is shaded with an additional dry rock wall, about 1 1/2 foot thick. The third side is adjacent to a shaded walkway, also located under the terrace. We have good experience using the water for showers and washing, but have not taken the somewhat risky step so far to drink it.
Traditionally, and also in this case, the inside of the tank is plastered and then covered with several layers of pure cement, "painted" onto the wall using a very watery solution. In addition to this, a watery lime solution, also traditionally used to paint the outside of most houses, is applied to the walls. The calcium has a disinfecting quality.
An external link to some pictures of the house is here.
The third picture in the left row shows the house and the terrace under which the water tank is located. The tank is in the foreground.