Rainwater Harvesting Is A Good Idea, But Complicated

In Western shoot-‘em-up movies you often see gunfighters hiding behind rain barrels for cover while firing at their enemies. Rain barrels were situated alongside most buildings in the Wild West of the 1800s to collect rainwater for drinking and bathing.

This raises an interesting question: Why don’t we do the same thing in today’s drought-plagued California to help alleviate water shortages?

So-called rainwater harvesting is a good idea and is widely used for irrigation in dry areas of the country. But while it happens in a few places, it becomes much more complicated when you try to tap rainwater for potable use.

Rain and snow are the ultimate sources of all drinking water on the planet. They collect in lakes and rivers and seep through the ground to aquifers that we tap with wells. Although they may absorb a few soot particles on the way down, rain and snow are some of the purest water sources to be found in nature.

The problem is that once raindrops and snowflakes hit the ground, your roof or a container, contamination occurs quickly and thoroughly. The barrels of rainwater that sustained so many early pioneers quickly became stagnant and filled with dirt, debris and pathogens. People back then put up with it because they had no other choice, but that’s part of the reason their life expectancy was so much less than in our modern era.

Nowadays we have codes and standards to assure that our drinking water is healthy and clean, and for that we should be thankful. Nobody wants to drink stagnant water filled with leaves, twigs, dust, dirt, bird droppings, insects, algae and other yucky material. Add to that microscopic parasites, bacteria, viruses and chemical contaminants that cannot be seen. So harvesting rainwater for potable use is only practical with thorough purification.

The wooden rain barrels of old have given way to cisterns made from a variety of materials,
including metal, wood, concrete, fiberglass or plastic. Plastic tanks, mainly polyethylene or polypropylene, are the most common material used for residential rainwater systems. They are lightweight, come in many sizes and colors, and are relatively inexpensive. Also, they can be made in an opaque, solid color to reduce the chance of algae growth. The American National Standards Institute (ANSI) has coordinated the development of various standards for cisterns and other products that are used to construct rainwater harvesting systems for potable water.

After you collect the rainwater comes the most complicated part of the system, treatment. A potable rainwater system should have both pre-storage and after-storage treatments in place. Pre-storage treatment consists of diverting or screening out organic debris before it enters the cistern. This reduces the amount of treatment needed after-storage, when you tap into the water for drinking and bathing.

After-storage treatment is the most critical part of the process. It requires sophisticated equipment to filter and disinfect the water coming out of the cistern, essentially mimicking what our municipal water authorities do to make water safe to drink before it enters your home.

Finally, home rainwater harvesting needs a distribution system of pumps, pressure tanks, piping and valves to provide water to your faucets and fixtures under pressure. If you plan to connect the rainwater to a municipal water system, local codes will require a backflow prevention device. All of this involves fairly complex plumbing. Designing and installing an effective rainwater collection and treatment system can be a costly, challenging task.

Also, rainwater systems have limited storage capacity. A family of four typically uses around 3,000 gallons of water a month. If little rain falls over a three-month period – which is characteristic of Southern California summers even in normal times – that would require a 9,000-gal. cistern, which is very large. Under our present drought conditions, storage would run dry very quickly. So around here you would no doubt still need to tie into your municipal water supply for the majority of your household needs. Melding the two systems together requires still more complicated plumbing.

As a plumbing company, we would love to see rainwater harvesting become widespread. It would provide us with loads of work. But as a practical matter its expense and complexity limits its residential market appeal mostly to areas without municipal water or reliable groundwater supplies.

Somewhat more practical are graywater reuse systems whereby water from washing machines, showers/tubs and lavs/sinks can be recycled for landscape irrigation, flushing toilets and other non-potable uses. I’ll tell you more about graywater recycling in my next blog.