Rain barrels, food grade, and the conversation we have every spring

From about March through June we get a steady stream of people wanting one tote for a garden. It is my favourite category of customer and the conversation is always the same four questions.

Question one: what does the water touch?

This is the whole decision and everything else follows from it.

The place people get it wrong is the middle of that table. Somebody buys a cheap unit for "just the garden" and the garden turns out to include tomatoes.

Question two: has it held a chemical?

If yes, it cannot be made food grade. Not by washing, not by bleaching, not by leaving it in the sun for a season. HDPE absorbs product into the wall and releases it back out slowly afterwards.

I say this plainly because the internet is full of advice to the contrary, and because the people asking are usually growing food for their own families. A thorough wash makes an ex-chemical tote look and smell clean. It does not change what is in the polymer.

Washing changes what is on the surface. It does not change what is in the wall. For a vegetable garden that distinction matters.

Question three: where will it sit?

Two things kill garden totes and both are free to prevent.

• Sunlight. Translucent HDPE in full sun grows algae inside and crazes outside. Shade cloth, a purpose-made wrap, or dark exterior paint all work. Dark paint raises water temperature less than people assume and the algae suppression is worth far more.
• Freezing. Above roughly the 35th parallel, a full tote that freezes splits at a bottom corner. Drain to a third over winter and it will last a decade.

Also: support the pallet at its four corners, never at the centre. A full 275 is 2,440 lb and a point load through the middle of a base will crack it.

Question four: what are you going to run off it?

Head pressure is 0.433 psi per foot of water above the outlet. On two concrete blocks a full tote gives about 1.6 psi at the tap.

Pressure also falls as the tank empties — the last fifty gallons deliver noticeably less than the first. Drip systems tolerate that well; pressure-compensating emitters tolerate it badly.

Roof sizing, since it decides how many you need

One inch of rain on 1,000 square feet of roof yields about 623 gallons before losses. Allow roughly 15% for splash, wetting and first-flush diversion.

Size for a single storm rather than the annual total. A tank that fills in one storm and gets used between storms does far more work than a huge tank that is never more than a third full.

The part that occasionally costs us the sale

When somebody describes an ornamental bed and asks for food grade because it sounds safer, we tell them a rinsed unit at half the price does the same job. A reasonable share of the time they buy the rinsed unit, and we have talked ourselves out of $150.

That is the correct outcome and it is also, over seventeen years, the single most reliable source of repeat business we have. People remember being talked down.

The full build — first-flush diversion, insect mesh on the overflow as well as the inlet, stands and linking totes into a bank — is on our rainwater harvesting guide.