Make a Pot Trough for Saving Water on Your Deck




In the great supercity of Auckland, NZ we now have to pay not only for the water that is reticulated into our property, but also for reticulating it out (the "wastewater charge" is based on how much comes in rather than how much goes out through the wastewater system, so even if you use most of your water on your garden, you still pay a wastewater fee). There is debate about the justice of this, but here's a way we're reducing costs by reducing the water coming in*. 

Watering potted plants is more efficient if they have trays under them, but the thirsty ones run out faster than the others. Putting them all in the same "tray" means they can share.
In our case, this project also helps hide the untidiness under the deck...

*We're also using our shower and bath water to irrigate a "compost biomass" garden (comfrey, sugarcane, culinary ginger, etc).

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Step 1: Materials and Tools

polythene (the thicker the better)
duct tape (gaffer, duck, etc)
hose fittings (see picture)

drill (preferably electric)
craft knife (although a decent pair of scissors would be better)
hose/watering can/bucket

Step 2: Prepare Deck and Build Frame

For this project, we started small as determined by the length between two deck uprights - enough for eight medium pots. I used timber I had to hand, but obviously you could make this look even better.

The deck need not be sanded smooth, but it is important to check for unseated nails, splinters* and rough spots. Naturally you should do this before building the frame, but hey.

*Cheapo deck timber, but has lasted over 20 years.

Step 3: Prepare Plastic Liner

Lay out your plastic, leaving plenty of overlap each end: remember that it has to fold up at each end of the trough. My plastic is 900mm wide, so is plenty wide enough for a double layer. If you have thicker plastic, you may only need one layer.

As my plastic used to be a painting dropcloth and had holes, I had to check it against the sunlight and stick bits of duct tape on the holes on the side that would not show.

Step 4: Lay Plastic in Trough and Check for Lowest End

You will need a lovely assistant. 
Fold the plastic in half lengthwise and lay it in the trough. Make the front edge sit about 1cm below the top of the front board and put in a staple 1cm  below the edge of the plastic, about 30cm from one end. Put in two or three more staples along that edge, but keep away from the ends (you will need room for cutting and folding).

Have a discussion with your gorgeous helper about which end is the lowest. Even though you're sure she's not right, loosely fit the plastic in place and pour some water in it. Gracefully admit you were mistaken, and lift the plastic to drain out the water. Use the dog's bone-eating-towel to dry the plastic - this towel will also be useful to kneel on*. This whole bit could be avoided if you use a spirit level beforehand.

* Three uses for the same towel. Points for the first one to make the obvious towel reference: extra points for the actual quote and book.

Step 5: Drill the Drainage Hole

Tuck the front edge of plastic well into the front board, then without moving that side, do the same with the rear board.
If you have two layers of plastic, carefully fold back the top layer, and stick on a 200-250mm length of duct tape folded back on itself so the sticky side is out. Press it on to the lower plastic layer above where the drainage hole is to go.

Carefully roll back the top layer and press it firmly onto the duct tape.

Stick two more short lengths of tape on the top plastic layer above the previous tape. This is all to make a firm base for the drainage fittings.

Use the holesaw guide bit to drill through all the tape and plastic layers into the deck. Do not let the saw teeth touch the duct tape.
Fold the plastic back and drill through the deck. Be cautious as you near the end of the cut as you could suddenly break through the deck and almost smack your head on the upper deck...

Step 6: Fit the Drainage Fittings

Centre the top nut over the small hole in the duct tape and mark around it.

Place a backing board behind the plastic and use the craft knife or scissors to cut a hole about 3mm smaller all around than the line you just marked.

Carefully force the hole over the top nut (so that the nut is poking through from the topside). If you are concerned about leakage, you may want to run a bead of hot glue or silicone sealer between the top nut and the upper duct tape before you screw everything together.

Firmly screw on the bottom nut and place the assembly into the deck hole.

Gently screw in the riser assembly. The riser can be made from anything with a thread that fits the top nut - in my case two adaptors gave me the approximately 50mm I needed. My top nut already had a rubber washer, but you will need to find one if your's doesn't. Or use thread tape.

Step 7: Finish Folding and Stapling the Plastic

Go around the trough folding and stapling the plastic 1cm below the top of the boards. I put a staple in every 200mm or so.

The corners can be tricky, and you may need to cut off some excess*. Remember, though, that the plastic will not be readily seen once the pots are in.

Remove any staples you may have used to temporarily hold the rear edge of the plastic.

* "Measure twice, cut once"!

Step 8: Place Pots in Trough and Water Them

Water the plants and note how much water you are now saving.

Put your tools away and tidy the workspace.

This trough allowed for eight pots with room to spare for wider spacing of the plants that need it - not planned, just serendipitous*. Taller plants, like the Bog Sage near the steps, would hide the under-deck mess better, but the parsley, sage and thyme** are easy to get at for cooking with fresh herbs.

* "The Three Princes of Serendip"
** "Scarborough Fair"

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    25 Discussions


    2 years ago

    I have lived in 4 different states in the U.S. It was always normal to charge a wastewater fee or charge due to the fact that the system worked to recharge or "clean" the wastewater. It wasn't till my family moved to Valdosta, GA did I have my 1st experience with septic tanks. A septic tank is usually located in the back yard, buried underground & attached to a house through the plumbing. All the outgoing water goes through it. I'm not sure exactly how it works but I know that solid waste doesn't come out just used water. It also has certain type of bacteria in it to break down the solid waste. There are also leech fields in the yard. They The septic tanks have to be emptied every 3-5 years depending on the size of the tank, house, # of people living in house. So basically for the 1st time starting in 2007 we only pay for water we use.


    4 years ago on Introduction

    Same rules here in Netherlands were I think I pay more for the water going out than coming in. Eventhough I use most of it on the garden. I think the only way out here is to have your drainpipes officially disconnected.
    Sadly there is no financial stimulus on saving water here as the water bill contains subscription fee, network fee, delivery fee local taxes, state taxes, watership taxes so te mojority of the bill is fixed and has no relationship to the amount of water you are using.. I have basically quartered my use,,,, but that is just a blip on my bill.
    Nevertheless, I save out of conviction and your ibble looks very interesting.
    I have a dripping slightly fawcett in my garden instead of replacing it... I put a plant under it


    5 years ago on Introduction

    Lasiandra stakes? Is that Salix Lucida Lasiandra (willow)?

    Good 'ible. Why the Wombles-in-Charge don't charge us by volume for water here in Christchurch, I'll never understand.

    1 reply

    6 years ago on Step 4

    it is (but of course) HHGTTG by the inimitable Douglas Adams- I could probably give you a page number (or even the episode from original radio series ) if we'd unpacked the boxes holding the book or the tapes yet!
    But what is a "dog's bone eating towel????"
    Like it, will adapt for my own planters

    5 replies

    Reply 6 years ago on Step 4

    And the winner is: jtpoutdoor!! Thanks for the comment, mate - I look forward to seeing your adaptations. The " dog's bone-eating-towel" is what protects our carpet from Molly's bone chewing. I'll post a pic in the next few days.
    Who will be first with the actual HHGTTG quote?


    Reply 6 years ago on Introduction

    Boy, I'm glad our kids/pups weren't in here to see the 'dedicated bone towel', they'd all want one of their own :). Great instructable. I have considered using half of a large pvc pipe in a similar manner.


    Reply 6 years ago on Introduction

    Thanks, rncbme. Molly knows we don't eat our bones on the carpet, but does "forget" now and then. If the bone's a good one then "On the mat. Molly, I said on the mat!" usually works, otherwise if the bone's already pre-chewed it's "Molly, on the mat. On the mat! Molly, I said on the mat! On The Mat!! Oh you stupid dog!!!" Then you chuck the bone outside while she wags her tail expectantly, waiting for whatever your about to get her that's better (which I don't of course).
    The large half pipe would certainly make the project simpler, but the curve would surely mean that a lot of the water would be out of reach of the roots, no?


    Reply 6 years ago on Introduction

    If you use pots this is true. My original thought was to fill the pipe with soil and plant something like strawberries. I was going to put rocks or gravel on the bottom of the pipe so the water could flow and the roots would not be prone to rot. Needless to say, I haven't actually done it yet. I'll let you know how it works out. Hello to Molly.


    6 years ago on Introduction

    In the state (Mobile, AL) we have a separate meter installed for things such as swimming pools and lawn watering. That way you don't have to pay a sewer fee on the water you use that is not processed back through the waste water system. Simple solution, otherwise you are being exploited by the powers that be.

    3 replies

    Reply 6 years ago on Introduction

    Nice! How do the authorities get around people who secretly divert water from the separate meter to the house system, like for flushing toilets?


    Reply 6 years ago on Introduction

    I am not sure about that one. But many homes have 2 or 3 separate meters for different uses. It seems the only logical and fair way to allow you to use water without stiffing you for the cost of the waste water plant.


    Reply 6 years ago on Introduction

    Our city in Texas requires you to put your pool on the home water just in case you ever pumped it out - ha ha. Only the sprinklers are to be attached to that meter a little savings.


    6 years ago on Introduction

    In the netherlands, where we have an abundance of water, we have that same system. Unless you can prove that you are not flushing the water throught the drainpipe, you have to pay about as much for disposing of the water as for getting the water. Though I try to save water out of principle, financially it is hardly rewarding as the major part of my waterbill is formed by duties, levies and taxes :-) Even when I when I halved my waterintake, it hardly made a dent in my annual bill.
    Nevertheless, your idea is a very good one

    3 replies

    Reply 6 years ago on Introduction

    Well, you're right, of course, diy_bloke. There are fixed charges for us too, but in summer the ratio for us drops dramatically from a winter ratio of 33% to a summer ratio of 20% (last month). I expect this month's bill to drop that ratio even further.
    Obviously, if one has to spend a substantial amount of money on saving water, one also has to work out the payback time. There are other factors to consider though, like what happens in a water shortage, lesser need for more water supply dams, rising costs of water, and so on.


    Reply 6 years ago on Introduction

    i understand. just that on a yearly base the fixed charges are so much bigger than the actual cost per liter, that the savings on water hardly make a dent. With water being about 1-2 ct per 10 liter (not sure exactly anymore) and me using 15m3/year is abt 15-30 euro per year on a 350 euro bill. I came down from 30 m3 so with simple measures (as the ones you propse) I saved about 15-30 euro per year.
    If I wanted to do some other methods, like using rainwater: a simple rainbarrel will cost me 180 euro's and will store 200 liters of water. 200 liters is 40 cts worth of water. Ofcourse I could use and fill it a couple of times say 10 times a year, that is 4 euro's per year, so it would cost me 45 years to regain that investment.

    Dont get me wrong, I applaud yr idea and I have been using similar idea's. Just wanted to point out that in some countries, any investrmant to save water is foolish. Therefore I just do it out of principle and on the cheap as much as possible.

    For other countries that ofcourse may be a completely different cost picture


    Reply 6 years ago on Introduction

    Yeah, sorry mate, I wasn't questioning your point, which is a very valid one. I've just had a look at our latest bill and our water is about 1.3 cents per 10L: given the current conversion rate, that's 0.01 euros, so about the same as you.

    As our fixed charges are a smaller percentage of the total, we stand to save more than you, as you suggest, especially since our water bill graph shows the two of us were suddenly, in January, using twice as much water (because of watering the veges and pots).

    The amount of money we'd save by using this project is small, but like you we do some of these things out of principle, and all the bits were free or already on hand.

    One major advantage of the trough, if we stop looking at the initial cost, is that the plants no longer wilt as easily, look good all the time, and we don't have to bother watering them as often; that's worth money in my mind!

    Thanks for the feedback.


    6 years ago on Introduction

    "A towel, it says, is about the most massively useful thing an interstellar hitchhiker can have. Partly it has great practical value - you can wrap it around you for warmth as you bound across the cold moons of Jaglan Beta; you can lie on it on the brilliant marble-sanded beaches of Santraginus V, inhaling the heady sea vapours; you can sleep under it beneath the stars which shine so redly on the desert world of Kakrafoon; use it to sail a mini raft down the slow heavy river Moth; wet it for use in hand-to- hand-combat; wrap it round your head to ward off noxious fumes or to avoid the gaze of the Ravenous Bugblatter Beast of Traal (a mindboggingly stupid animal, it assumes that if you can't see it, it can't see you - daft as a bush, but very ravenous); you can wave your towel in emergencies as a distress signal, and of course dry yourself off with it if it still seems to be clean enough.

    1 reply

    Reply 6 years ago on Introduction

    There it is: the quote itself! Points. Take a look at dustoof's comment, also, for what is probably an exhaustive summary of HHGTTG towel references.