The Wattworks system is a waste water recycling system developed in Melbourne, Australia. (You can also find Steve Watts in your telephone directory - in Balwyn if you are interested).

PLEASE FORWARD YOUR ENQUIRIES ABOUT THE WATTWORKS SYSTEM TO WATTWORKS DIRECTLY - WE DO NOT MARKET THE BASE PRODUCT OURSELVES - JUST HAVE AN INTELLIGENT CONTROLLER. AS MENTIONED ABOVE Wattworks or you could try Going Solar.

The system consists of a water tank, a submersible pump, a set of floats and an electronic controller.

It takes water from the bathroom and laundry and stores it for later use. The stored water is then used to flush the toilet and to water the garden. The controller empties the Wattworks every 24 hours, and responds to flushing the toilet by refilling it. Parts of the garden are watered when the tank is emptied OR when it is overfull - via a range of watering runs spread throughout our orchard. It was a perfect solution for us - with our inability to install a composting toilet, an existing septic system and a desire to use the water that we do have in a more practical way.

Nothing really.

We didn't have any input into the Wattworks system, other than purchasing one for recycling our waste water. What we did do was realise that the controller used didn't quite fit our requirements, so we built an alternative that may be of interest to other people. We ended up designing and building an alternative solution that was easier for us to use, more effective and had the added benefit of being able to be viewed and controlled remotely.

Why was the controller a problem for us

The current controller uses industrial 24VAC relays and hardwired logic to drive the 240VAC pump and the 24VAC solenoid valves used to divert water to either the toilet cistern or the garden. A rather expensive 24VAC timer with a 5 day backup completes the picture. This form of control is not very flexible, in that changes to the logic require changes to the wiring.

When you want to set the clock (which has a 15 minute resolution) you need to open the weatherproof cover and use a tool such as a screwdriver. This is not ideal as you are within 2" of the 240VAC lines.

The timer sets the empty time (due to EPA regulations the water must be emptied every 24 hours). This time is inflexible, in that it doesn't take into account that we like to sleep in on weekends and sometimes during the week we have to get up early to get to the airport. Another problem with the timer is that even if the tank is emptied, until the timer on period expires any new water added to the tank will also be emptied out.

Other problems are that when the tank is empty but someone flushes the toilet, it turns on the toilet cistern solenoid, but doesn't turn on the pump until there is some water to pump. This means that the solenoid is using energy (albeit not a lot) when it doesn't need to and could result in a shortened lifespan for the solenoid.

When the water is emptied and you want to use the toilet you are out of luck. This is the case even though the low-water sensor leaves about 1 1/2" of water in the bottom of the tank.

When the water level hits the high water mark, water is pumped to the garden, which is fine, but it does this regardless of the time of day. In Australia in summer this simply means wasting the water as it will evaporate more quickly than it can be absorbed and can be detrimental to the very plants you are trying to help.

We decided that we could improve the reliability and the energy saving of the system by replacing the relays and hardwiring with a microcontroller-based system. This system uses solid-state components to switch the AC for both the solenoids and the pump. The controller is smaller, lighter and much more capable than the original.

In addition we chose to using a "Window of Opportunity" model for selecting the empty time. This works by having a start time that is before the usual waking time and an end time after the latest reasonable time you would arise. If the toilet is flushed at any time during this period then we initiate an empty out of the tank after refilling the cistern. If you don't get up until really late then the tank will be emptied at the end time.

We then coupled this by using the un-emptied amount of water as a reserve capacity to refill the toilet cistern until the tank begins to fill. By using a timing mechanism to determine the number of flushes we can support we can provide far fewer outages where there is insufficient water to flush the toilet than the original controller.

To counteract the problems with water evaporation we added a safety zone for garden watering. The watering triggered by the high-water mark is only allowed within a defined period. The default is from 10:00pm to 10:00am. This cuts out the hottest part of the day ensuring the most effective use of the water.

No solenoid is activated unless the pump is also activated. This makes sure no energy is being wasted and components aren't being used when they don't need to be. Safety cutouts make sure that should anything happen the system will automatically reset itself, turning the pump and all solenoids off, until it asseses the impact of the problem.

All the options are user-configurable. This includes the start and end time for the empty out period, the start and end time of the garden watering period and the timeout value used for the reserve capacity. There is even an option that allows you to cope with the cistern float switch being installed upside down!

To top it all off we then added a web interface to the controller. You can check out how the Wattworks is performing at any time of the day or night.