Overview

The rainwater harvesting system feeds toilets and a tap in the utility room by gravity from the 100L rainwater header tank in the attic. The washing machine also currently uses rainwater for its cold feed.

When the level in the header tank drops, a sensor tells the controller to open the valve from the underground storage. If RW is available, the pump runs to fill the header tank. Otherwise the header tank fills from the mains.

The pump is pressure-sensitive. When the outside standpipe tap is opened, the pump detects this and runs, pumping from underground storage directly to the standpipe (not via the header tank).

The system is powered on its own circuit (labelled on the consumer unit) and there is an isolator switch for this circuit in utility cupboard (in no.74; check no.72)

Controller

The controller is at the left end of the utility worksurface in no. 74, and in the utility cupboard in no. 72.

I have not found a full description of what the flashing lights mean. Generally we should leave it in rainwater mode, but there is also holiday mode.

A Refresh function is available if you want to flush the system through with mains water for any reason. It empties the header tank and refills it with mains water.

The system automatically does a refresh once a week, as a safety measure against disease build-up. A refresh also seems to clear air locks.

There is a small filter in the controller. Open the controller door to get at this.

Airlocks

We have occasionally had airlocks in no.74, detectable by noisy pipes and toilet cisterns refilling slowing. We have found two ways to resolve an airlock:

• In the attic, remove the cover from the header tank, and loosen the cap, allowing the air to bubble out, or
• Press the Refresh button on the controller.

Here is Simon the plumber showing how to loosen the cap:

Filters and maintenance

The system currently has two filters:

• In the pump unit, and
• in the controller

Both need cleaning every 3 months. Record when filter cleaning has been done on the sheet kept with the special lifting tools.

The pump unit filter is accessible by lifting a patio slab with special tools.

Do not lose the special lifting tools which are kept near the controller.

Remove also the black plastic drain cover.

Lift the clear plastic filter from the yellow pump and flush the crud from (you could use the standpipe). I found an old dishwashing brush and toothbrush useful.

The controller filter is accessible by opening the white plastic cover of the controller unit. Turn the isolator switch off to prevent it pumping. Hold a vessel under the controller unit and gently unscrew the filter. I have not done this myself – I’m a bit scared of doing it. I just watched Simon the plumber do it.

Perhaps we should add more filters. There could be a sieve filter sitting in the top of the downpipe on each extension. There could be a sieve filter hanging at the bottom of each downpipe descending from the old roofs.

Gutters

Keep the gutters clear. Iain did this for us April 2024, reporting a lot of builders’ crud in no. 74 gutter. No. 72 gutter was pretty clear although water pools at the house end so the drop is not correct. I predict that the main source of gutter blockages will be moss falling off the tiled roofs.

Maintenance

Other than cleaning the gutters and filters, in theory the system runs itself. However silt might build up in the storage tank on a decades-long timescale. Somewhere I saw a note about pumping this out if necessary. I’ll write here if I find that again.

Isolating the header tank

If it should be necessary to stop the flow from the header tank, turn the valve just below the tank as shown here:

Manuals, support and warranties

The paper user guide etc for RWH is in a box file, which is is currently in the no.74 kitchen cupboard next to the fridge. The builders threw away the delivery notes and order info but I rescued some of these from the pile of crap they left in no.72 kitchen drawer. These might be important for proving warranties. These rescued documents are in no.74 office, an unsorted pile including A3 drawings. I think they’re on the shelving unit.

The suppliers do telephone support, not site visits.

This is the supplier’s specification and parts quotation. We chose Option 2 with the 3000L tanks. Note the “Extended two year guarantee” on the Hydroforce pump:

Here is the installation manual:

April 2024: I wonder if tripping the RCD at the consumer unit was associated with failure of the pump. But another thing we should check is the controller filter: it might simply need cleaning, but has not been checked since Simon the plumber did it last summer (when he found the plastic shards in the system caused by Grantchester incompetence).

Washing machine feed

If residents do not want to use RW for clothes washing, they can get a plumber to swap the cold feed to mains rather than RW. The mains pipe extends close for this.

These photos should help swapping the feed in no.74:

If you swap the feed in no.72, do not change the hot inlet, as that comes from the hot water tank, taking advantage of no. 72’s solar hot water system. Cold RW feed is blue; hot feed is red:

Utility tap

Must be clearly labelled as rainwater / not for drinking. I use it for hand washing clothes. By design it looks very different from the mains tap.