Introduction: Grey Water Re-use System

In my community, there's currently a water management problem (lots of water in the river, and rain in the winter, but not enough storage capacity for drinking water through a dry summer). The municipality introduced a 4-stage plan to save water : Water Shortage Response Plan. In stage 4, all garden watering with tap water is prohibited. Also, our water use is metered.

It seemed like it might be a good idea to collect grey water for garden use, providing it was not too expensive in materials or time, and did not involve buckets or hosepipes running across the bedroom.

I decided to target the master bedroom bathtub.

Step 1: Map the Existing Plumbing

The concept was to divert waste water from the bathtub drain, before it was mixed with detergent-laden water such as laundry waste, or toilet effluent. So I had to identify the correct pipes. In my house, the plumbing is all concealed (normal for Canada). I had identified an inspection hatch which I thought was a mix of bathtub and washbasin waste, but on investigation (feeling the pipe while running hot water) it proved to be only washbasin waste - not enough volume to justify the effort. Mapping with a thermal camera located a downpipe inside an interior wall that was carrying bathtub waste, but luckily the geometry was unfavourable to cut into that and I continued to investigate. More measurements suggested that the pipework was probably concealed in a lowered ceiling above a cupboard, and a hole cut in this proved this correct.The downpipe in the wall included toilet waste, which I did not want.

Investigation revealed the following: a vertical pipe from the bathtub drain to a U-bend, which fed into a larger diameter pipe along with waste from a shower, and toilet waste. The section of pipe above the U-bend was accessible and long enough to fit an inline ball-valve.The geometry of the walls made it possible to run a diverter pipe along the ceiling space, through a wall to the garage, then through an outside wall, without disturbing the interior finished walls.

Step 2: Purchasing Materials

One goal of the project was to save money on water. Accordingly it did not make sense to install a system with a 20-year return on investment, such as fully concealed 2" ABS piping behind new wallboard. I chose the following:

  • Covered rain barrel, subsidized by the municipality - about $35
  • 2" PVC ball-valve - about $12
  • 1/2"I.D. PVC pipe and corner fittings for the diverter pipe
  • Standard garden hose tap to mount on the outside wall
  • 1/2" drip irrigation black connector hose to the rain barrel

I picked PVC electrical conduit instead of the more expensive potable water quality PVC, and irrigation pipe instead of the garden hose I had originally planned. The irrigation pipe is more fragile and designed to be fixed in place (which this is), but has a smaller outside diameter and is less obtrusive as well as being less expensive. Since at this point the hose run is outside, potential leaks are not an issue.

Step 3: Assembling the Diverter

I was able to unscrew and remove the section of 2" ABS pipework including the U-bend, which made work much easier. I had anticipated having to insert the valve in situ, and had elected to create a T-junction rather than purchase a pre-made one which would have to be inserted inline. In the event, there may not have been room in any case.

I marked off a fixed distance on the pipe, and removed a section corresponding to the inline length of the ball valve. I created a PVC collar from a butt join piece, and drilled a hole to take a 3/4" pipe. I drilled another 3/4" hole in the ABS pipe, and slid the collar over the ABS pipe so that the holes aligned. The PVC collar was glued to the ABS using ABS-PVC transition cement. The resulting hole through both layers was thus deeper and more secure than just a hole in the ABS pipe. I secured a PVC right-angle joint in the hole with transistion and PVC cement. The ball valve was glued inline using transition cement. I then re-fitted the modified assembly to the bathtub drain and the original plumbing stack. The diverter pipe has a short vertical section, then another right angle, then a downward sloping horizontal section through a wall, and a final horizontal section to a tap on the outside wall.

From the tap,the irrigation hose leads to a hole drilled in the lid of the rain barrel.

In use, the ball valve is closed and the hose tap opened, allowing bathwater to drain into the barrel. When not in use, the ball valve is opened allowing bathwater to flow unimpeded to the original sewer connection. The U-bend prevents vapour from the sewer system from escaping into the bathtub, as before.

One issue appears to be that the bathtub drain was never intended to hold a head of water - the metal drain is inserted about 2" into the ABS pipe, rather than having a completely water-tight join. There have been a few drips.

The rain barrel also functions a a normal rain barrel to collect water from the roof, for when we do have rain.The overflow leads into the original gutter downpipe. A pre-fitted tap allows a garden hose to be connected, or water to be drawn off into a watering can.