Rainwater and greywater are two terms we’re hearing more often amongst the eco-conscious—especially when it comes to do-it-yourself (DIY) water conservation for the home and garden.

Rainwater collection and greywater reuse are wonderful ways to nourish a garden while making the most out of every last drop of water. But it’s important to understand that rainwater and greywater are not the same. Their applications are complimentary, but they are different.

The difference between rainwater and greywater

Rainwater is fresh precipitation straight from the sky. Completely free of salts, chemicals, pharmaceuticals, and minerals; it’s naturally pure, and the cleanest water our hydrologic cycle offers. Of course to get that water into rain barrels or tanks, most of us collect from the roof, which means there’s some accumulation of organic matter. But by all accounts, this water (organic cooties and all) is universally appreciated by a thirsty garden. In fact, rainwater is the absolute best water for your plants. To your plants, those cooties are fertilizer!

Greywater is once-used household water, discharged from washing machines, showers, tubs, and bathroom sinks. This can also be a great source of irrigation water if the household uses greywater-safe products. You’ll notice kitchen sinks aren’t on the greywater list. Kitchen sink discharge is considered blackwater because of the bacterial load (think raw meat!). So in sum, you can think of greywater as “everything but the kitchen sink” (and of course the toilet).

How do I irrigate with rainwater vs. greywater?

This home uses rainwater for the drip-irrigated edibles, while greywater serves the fruit trees and medicinals around the perimeter.

Rainwater

Because rainwater is relatively clean, it can be stored safely for long periods of time and released at the gardener’s discretion. BlueBarrel offers an affordable DIY multi-barrel rain barrel system, made from recycled barrels! Particulates are filtered out on the way into the tanks, cisterns, or barrels, so the water doesn’t contain anything chunky that might lead to growth or clogs.

Many people use stored rainwtaer to hand-water potted plants (which are particularly sensitive to salt and chemical buildup from other water sources); or to irrigate garden beds—even edibles!—through a simple gravity-fed drip irrigation line.

Greywater

Greywater, on the other hand, is not recommended for storage and is best distributed directly onto the landscape (released a couple of inches below the soil’s surface). Complex greywater systems may include surge tanks to gain a little more control over distribution rate, but an automatic pump is used to keep that water cycling out at least every 24 hours—lest it become blackwater!

The Laundry-to-Landscape (or L2L) setup is one of the more popular systems for DIY greywater gardeners, and in many areas can be done without a permit. Laundry discharge is diverted through a pipe that leads out of your house and directly into a series of mulch basins in your garden.

Because greywater contains lint and suds, it is not recommended for potted plants or for drip irrigation lines (that’s what rainwater is for!). That said, it’s a wonderful water source for less sensitive perennial plantings, shrubs, vines and trees—even fruit trees. In sum, greywater is great for plants that can handle the irregular flood-load of water that comes when you do laundry, and that won’t suffer from the stuff in the water.

What about showers and sinks? Whereas laundry discharge can be intercepted without cutting into any potable plumbing lines, sinks and showers are a different story. Many people collect greywater from sink and shower drains but these systems require a permit in most jurisdictions, and often require the help of a professional.

Can I incorporate rainwater AND greywater in my garden?

First of all, if you’re asking that question, you’re awesome. Bravo!

You can and should incorporate both rainwater and greywater into your eco-paradise. In fact, they are ideal in tandem (see the photo example above).

Since rainwater and greywater have different properties and are suited to different kinds of plants and irrigation strategies, you can maximize your efficiency by using both—but we recommend you think of them as two separate systems.

For example:

Imagine an edible garden served by hyper-efficient drip irrigation, surrounded by a gorgeous border of perennials, medicinals, pollinator attractors, flowering vines, and fruit trees. Potted plants bring life to the inside of the home. (Perhaps this sounds like YOUR garden!)

Now add a series of rain barrels (ahem, a BlueBarrel System!) to service your drip irrigation line clog-free (yes, rainwater is suitable for edibles!), and for hand-watering those sensitive potted plants.

Next, redirect your laundry discharge (greywater) around the border where you have shrubs and perennials that will handle the flood-load. The greywater gets a push from your washer’s pump, so it can make it around the border.

THE “GREY” AREA: shower warmup water

It’s worth mentioning that shower warmup water is in a category on its own. (This is the potable bounty that us water-geeks collect in buckets while we wait for our showers to warm up…) 

Many think of shower warmup as greywater, and it certainly is greywater once it hits the drain. But if we intercept it in a clean container, this is actually potable water with many potential reuses. I personally use my shower warmup to flush the toilet, only because it’s right there.

But shower warmup water can be stored along with your rainwater, and we’ve had quite a few BlueBarrel customers do just that. Shower warmup water can be directed out the bathroom window through a hose that connects directly to a vent on your BlueBarrel System; or you can use a funnel to pour this extra water in by hand.

In conclusion…

You should do rainwater and greywater, but you shouldn’t combine them into one system unless you’re a pro. But then again, if you recognize that the ideal uses for rainwater and greywater are so compatible, you may still achieve your best and most sustainable design by employing the two systems side by side.

HOW TO:

DIY rainwater harvesting resources:

• BlueBarrel Rainwater Catchment Systems
• Brad Lancaster’s Rainwater Harvesting for Drylands

DIY greywater resources:

• Greywater Action
• Oasis Design