Rainwater Harvesting

Rainwater Harvesting, as that term is used here, refers to catching and sequestering rainfall runoff from roofs and utilizing that water as a supply source, to augment or displace supply from the “normal” water system. A more “proper” term for this practice is building-scale rainwater harvesting, since almost every water supply system in the world is a rainwater harvesting system. Most of them utilize rivers, lakes, reservoirs or aquifers as the storage “cistern”. They differ from building-scale rainwater harvesting only in how long, indirect and convoluted the connection is between the rainfall and the end uses, so they essentially differ only in system scale.

In a building-scale rainwater harvesting water supply system, that connection is very direct. Typically this strategy entails collecting rainwater off building roofs and routing this water to a cistern, perhaps integrated into the structure of each building but certainly “associated” with that building – e.g., a free-standing cistern on the same lot. Each building would therefore incorporate a self-contained water supply system, including all facilities required to filter/treat/disinfect the water so that it can be used to supply all water demands—including potable—within and around that building.

This “decentralized concept of water supply” can offer various benefits in appropriate circumstances. The documents in this menu describe those benefits.

Rainwater Harvesting as a Development-Wide Water Supply Strategy

Excerpted and adapted from a proposal I submitted to plan and design the water resources infrastructure for a development near Austin, Texas, this paper reviews the building-scale rainwater harvesting strategy for that context. The paper offers a rundown on general advantages relative to other water supply options, provisions for an assured backup supply during periods of drought, an idea for cost-efficiently incorporating increased roofprint and the storage cistern, and a review of a modeling process to aid in maximizing the efficiency of the overall system.

Rainwater Harvesting Model

A model I developed can be used to analyze building-scale rainwater harvesting systems. This model is reviewed to illustrate how the system can be optimized to serve the projected demands, or alternatively to see what portion of demands could be served by a system of given configuration. Options include modeling interior water demands and/or irrigation demands, curtailing demand during drought, and routing interior water use – through an appropriate wastewater system – to satisfy irrigation demands. The model observes the system “behavior” over 20 years, using the historic monthly rainfall totals for the location being modeled, to provide a projection of how the system would perform in the future over a range of conditions.

The “Veranda Strategy”

Review of a design strategy that adds verandas to the exterior of standard house plans to cost efficiently provide additional roofprint. The veranda surface area can be large enough that required cistern volume is provided by a relatively shallow excavation underlying the verandas. This design concept creates what I call the Hill Country rainwater harvesting vernacular house design.

Contact Info for David Venhuizen, email: waterguy@venhuizen-ww.com waterguy@venhuizenww.com