Sophisticated graywater recycling equipment has opened up possibilities for water re-use, but a $200 washing machine gadget may be your best investment for residential graywater.
We recently had a client approach us about recycled water, understandably wanting to do their part to conserve this precious resource. They envisioned gathering sink and shower water and using it to flush toilets. While this is certainly doable, the number-crunching tells a different story that ends up saving money and effort.
First, here is a re-cap on what is allowed in California: Graywater can be collected from laundry, showers and bathroom sinks. Kitchen sinks, dishwashers and toilets generate blackwater, which must go to the sewer or other treatment, but graywater can be collected for re-use. Untreated graywater must be used within 24 hours, or it becomes “blackwater”, so if it needs to be stored, it must be treated to a high level. Graywater used for landscape irrigation does not require treatment as long as it is distributed below the surface (e.g., underneath at least 2” of soil or mulch).
Starting at a few thousand dollars, water treatment can make sense at the scale of a hotel or multi-family project, but for a single-family home, the appeal of using graywater directly becomes apparent based on the example calculations below.
Let’s look at some numbers, assuming a 4-person home and water-efficient devices:
Toilets are so efficient now (as low as 0.8 gal/flush) that treating graywater for flushing just doesn’t pencil out. It’s also notable that even if you have lots of showers and laundry to generate graywater, you’ll still need to supplement your irrigation with potable water.
Although showers may generate more graywater, there are a few big advantages of laundry-to-landscape (L2L):
· The washing machine is already pumping out the waste water with enough pressure to distribute to your landscape – no additional pumps or tanks needed in most cases
· Laundry water is generated all year
· No building permit is required.
For showers, you’ll likely need a surge tank and a pump, and a building permit is required.
For L2L, efficient implementation requires advance planning because you either need the laundry machine to be on an outside wall or you need to plumb the waste line under the slab in the first place. L2L retrofits are pretty easy if the washer is on an outside wall or you have a raised foundation. The device is basically a 3-way valve that can divert graywater to the irrigation or be manually switched to the sewer, just in case you have a bleach load that you don’t want routed to your plants. To avoid clogging drip emitters, laundry water is usually targeted to trees or bushes. Materials are $150 - $300.
Although L2L is pretty common now, we predict that re-use of shower water will be on the rise, along with new waterless technologies for toilets. As we move toward water conservation goals, we’ll be using every tool in the toolbox. Net zero water, anyone?