Free Idea #1: Saving water

I’m adding a new category of posts, titled “Free Ideas”. These are brainstorms that might actually have some real-world value, but that I am not in a position to do anything with. Feel free to run with it…

The issue

Given the plethora of well-documented world-wide issues with adequate fresh water, it occurs to me that it is practically obscene to be using clean, potable water for the purpose of whisking bodily wastes into the sewage system; that is, flushing the toilet. My back-of-the-envelope calculation suggests that the US wastes 4.8 billion gallons of water per day in this manner (partial statistics here). You could save a lot of salmon with that kind of flow. Low-flow toilets are not a complete solution, since each flush still wastes 1.6 gallons; moreover, in the city of San Francisco, they have a problem with inadequate volume of liquid to move the wastes through the sewers, which were designed for older high-volume toilets (yeah, I know… TMI).

The solution

My idea is to revise the building code to require the use of gray water for flushing toilets. Gray water is recycled water; for example, recovered from the shower or bathtub. This water is already ticketed to go down the drain, and you can’t really argue that a little shampoo residue is going to hurt your toilet bowl (a filter could be used to catch the gross stuff like hair). In drought situations, a lot of people already capture shower water in a bucket and it it to flush the toilet. My idea is to institutionalize this with a standard design of a simple plumbing system that would perform the same function, and be completely transparent to the user.

A typical shower using a modern 2.5 gallon-per-minute shower head would provide 7 or 8 gallons of water for this system. For comparison, a modern low-flush toilet uses 1.6 gallons per flush. So for each person taking a shower in your household, you would get five “free” flushes per day. It would also be logical for the system to utilize water from the bathroom sink and kitchen sink (assuming no garbage disposal), and possibly the dishwasher and washing machine. Gray water irrigation systems don’t use washing machine output because of the possibility of fecal contamination from diapers (more TMI), but that”s not a problem as this water would wind up in the sewer anyway.

As I see it, this system would need a holding tank (probably about the size of the typical water heater), and a system of valves that would automatically enable flushing with clean water if the tank happened to be empty, and that would route excess gray water down the drain when the tank was full. It might also need some kind of pump or siphon system depending on the relative levels of the plumbing fixtures, and a cleanable or replaceable filter. Some genius could probably design a kit that could be used to retrofit existing residences.

Comments are closed.