Potable Water From Rainwater

Since one of our friends (Justin G who is doing the off grid tiny home thing in ‘Lutra) asked about it recently, here is a recap of our rainwater filtration system at Rally Creek.

Over the past summer, we built and tested a filtration system for our 1200 gallon rainwater catchment up at Rally Creek. We finalized the initial build at the end of the summer and have had the opportunity to test the water from the system to ensure it is “safe for drinking”. The testing done using retail water test kits shows no harmful bacteria and all harmful contaminents such as heavy metals are virtually zero. Only the pH was slightly out of normal municipal drinking water range as “slightly acidic” but still way less acidic than most beverages (soda 3.0 pH, lemonade 2.5 pH, etc.). Typical drinking water runs 6.5 (slightly acidic) and 8.5 (slightly alkaline). Ours was typically testing around 5.8 or slightly higher.

Our Setup

You can find product links in our UV Filter Created Drinkable Water and Rainwater Filtration System for Drinking Water articles.

Filtration is the key to the system. First with the sediment filters to take out large particles and make the work less “taxing” on downstream filters. Then some carbon and heavy metals or salt filters, and lastly a UV filter. The UV filter is the key to killing harmful bacteria.

In our system we chose a “whole home filtration system” as we intend to provider water for two families, one in an RV and the other in our tiny cabins. We don’t anticipate heavy water usage, but in the hot “upstate summers” at Rally Creek, drinking water and a quick cold shower at the end of the day will be in high demand.

Stage 1 : Rainwater Debris Filters

These are basic screens set at various points on the gutter intake system. There is also a filter at the head-end of the rainwater catchment that will bypass large debris and let water flow into the tanks. This takes out the big stuff like sticks or leaves.

The water goes from here into a series of rain water holding tanks (5 of them, 250 gallons each). The water flows out via PVC (and/or Pex currently but we are going 100% PVC to the “pump house” this summer).

A rainwater pump with and automated low pressure and restart controller is used to move the water from the tanks and pressurize the system to push it through the filters and out the final shower head and spigot.

Stage 2 : Spin Down Filter

We put this in after the pump. The spin down filter catches any large debris that may not have been filtered by the screens.

We current have this after the pump, but will likely add a second one just before the pump to help reduce future pump maintenance.

Stage 3 : 3-Stage Whole Home Filter

We went with a whole-home filter next. This is a oversized version of a carbon filter you will find in most fridge filter systems or a pitcher-based filter. It is a much larger size allowing more water flow and minimal pressure reduction. However in this case we have THREE filters, not just one carbon filter. The carbon filter is great at catching most large molecules including carbon and various metals as well as organic matter. From there is passes through a secondary filter to catch smaller molecules, these are the rare but more harmful toxins you read about. Lastly is the speciality filter, we chose a lead filter as that is in the kit that was on sale at the time (we don’t really need lead filtering) but will eventually buy a salt filter and put that in place instead — though neither lead nor salt are a big concern at this location as rainwater tends to not carry either pollutant.

Stage 4 : UV Filter

We use a plug-in 110V UV filter. Thankfully this is low amperage and has an auto-off feature so the UV bulb is only on when the water is flowing. The length and design of the tube provides enough UV exposure to kill any harmful bacteria that gets through the filters. E Coli is one of the biggest concerns due to the animals (birds & squirrels mostly) that may use the roof of the rain catchment system as a latrine. We mount the filter vertically (input at the bottom) to increase the exposure time by a marginal amount. Horizontal mounting is also viable and tested safe by the manufacturer.

Last Stage : Potable Water From Rainwater

Out of the other side of the UV filter comes clean potable water. We use this primarily for washing ourselves and the dishes at the moment, but after several tests I am confident enough in the results to drink it. It is certainly cleaner than “backyard hose water” I drank from as a kid and way cleaner that stream water with a water tablet dropped in. We will get the water tested at a lab this spring to convince my wife we won’t all get Ebola from it and stop lugging up a few gallons of water to the site every time we visit.