For this reason, this type of rainwater harvesting system is particularly recommendable in districts with high population densities, such as (in Barcelona) Sants, Verdun, Sagrada Família, Sant Antoni or el Guinardó, whose consumption of resources per m3 is up to 40 % lower than that of districts like Pedralbes, Sarrià, la Clota, el Bon Pastor, Vall d'Hebron or Vallvidrera. (sciencedaily.com)
Also consider for rainwater collection for small farms that uses rock cisterns, pits lined with clays, graded gravel to ballast rock and capped with clays to reduce evaporation; these don't need concrete & steel, ballast rock is 40 % voids for capacity. (climatenewsnetwork.net)
Features of this landscape include the use of rainwater collected in downspouts and rain barrels for plant irrigation and fountain sculptures. (phillywatersheds.org)