Look at that picture properly before reading on, and try to answer three questions. What could that waste do to the health of the people walking past it? What could it do to the cow standing in it, which will eat plastic it cannot digest? And why is it lying in the street at all?

The last question has an answer that is worth knowing, because most people guess wrongly. That pile is not there because the people who live around it are dirty. It is there because nothing in it was separated. Everything in that heap was thrown into the same bag, so the vegetable peel and the plastic wrapper and the broken glass all arrived together, and now nothing in it can be used for anything. Almost every waste problem you will ever see begins at that moment, in somebody kitchen, and not at the road.

Some waste rots and some does not. Waste that living things such as bacteria and fungi can break down is called biodegradable. Vegetable peel, food scraps, paper, leaves and cloth made from cotton are all biodegradable. Waste that they cannot break down is called non-biodegradable, and plastic, glass, metal and rubber belong there. Only by managing the two kinds in two different ways can the environment be kept clean and balanced.

Now here is the part that matters more than the two definitions. Keep them apart and both are useful. Mix them and you destroy both at once.

Read the last column again. Neither of those two results is anybody being lazy at the roadside. Both were decided in a kitchen, by whether there was one bin or two. That is why separating waste where it is produced is the single most valuable thing an ordinary household can do, and why it costs nothing at all.

Solid waste is managed very effectively by the method known as the three Rs: reduction, re-use and re-cycle. Almost everybody can name all three. Almost nobody notices that they are written in that order on purpose, and that noticing it changes what you do.

Ask most people which of the three is best and they will say recycling, because that is the word everybody has heard. Recycling is the worst of the three. It is still far better than throwing something away, but it is the last one you should reach for, not the first.

Read the last column downwards and the ranking explains itself. The best answer is the one where nothing had to happen. Notice too that this is the same idea the whole unit has been built on. Depletion begins when we take faster than nature replaces, so every one of the three Rs is simply a way of slowing down the taking. Reduce slows it most, because the resource is never taken at all. Recycle slows it least, because the material was already taken and you now spend energy to use it again.

Reduction means being careful with natural resources and cutting down the use of things that pollute the environment. Choosing a bag that can be used again and again when you go to the market is reduction. So is leaving unnecessary packaging at the shop instead of carrying it home. If we use less plastic, demand for plastic falls, and when demand falls production falls with it, so less harm reaches the environment. This is the quiet power of the first R. A shopper changes nothing except a habit, and a factory somewhere makes less.

Reduction applies to farming too. Chemical fertiliser should be used less, and the use of pesticide should be brought down steadily. In their place, compost manure and methods that use living things to control pests should be used. If that sounds familiar, it should. This is exactly the way out of the fertiliser loop from the last topic, where each year of heavy chemical use weakened the soil and forced still heavier use the year after. Compost rebuilds the small living things in the soil instead of killing them, which breaks the loop rather than tightening it.

Re-use means taking something that has already served one purpose and using it for another instead of throwing it away. Clothes you no longer need can be given to somebody who does need them. Old and worn clothes can be joined together to make pillows and mats, and old cloth can be put through a machine to produce cotton for quilts and mattresses. A glass bottle from the kitchen can hold sugar, tea leaves or salt. A plastic bag can be used many times. A milk packet can be filled with soil and used as a pot, and a drink bottle can be cut open to make a planter. Taking the same bag to the market again and again is re-use as well as reduction.

Re-using a thing lowers the demand for it in the market, so less of it needs to be produced, and the harm that reaches the environment falls.

Re-cycling means taking old materials that have already been used, treating them as raw material again, and making new goods out of them. Old exercise books and books can be taken to a paper mill and made into paper again. Goods made of iron, aluminium, copper and brass can be melted down when they wear out and cast into new vessels. Even the offcuts left over from making metal goods, along with scraps, rods and lengths of wire, can be melted and used again.

Recycling is genuinely valuable and it should be done. It is only worth being clear about why it comes third. Every recycled object has to be collected, carried, sorted and then heated hard enough to melt or pulp it, and all of that takes energy that reduction and re-use never needed. Paper also comes back slightly worse each time, because the fibres are cut shorter in every round, so a sheet of paper cannot go on being recycled forever. Metal is the great exception, since iron and aluminium can be melted again and again without losing much, which is why scrap metal is always worth money to somebody.

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