26 million people across England and Wales were just told they can’t water their gardens with a hosepipe.

It's a strange sight in a country famous for rain and grey skies.

Meanwhile, across Europe, the Rhine, the Danube, the Po, and the Loire rivers are all sitting at record lows, and we are baking through our fifth heatwave of the summer.

Almost exactly a year ago, I sent an email about running some water math. Back then it was back-of-the-envelope theory about how much water you need. This summer, the envelope is on fire.

So let's run the math again, specifically aimed at garden needs.

Say you've got a "tiny" 1,000-square-foot (100 m²) garden. That’s merely 10 paces on one side and 10 on the other. That’s your small garden.

At the recommended watering rate of one inch (25 mm) per week, that's roughly 600 gallons (2,270 liters) every time you water - about 2,400 gallons (9,000 liters/9 m³) a month.

Let’s say you’ve got a 5,000-square-foot (465 m²) garden instead. Now you're at 3,000 gallons (11,350 liters/11 m³). Per week.

And if your plan for supplying that water is "the tap"?

You now have 26 million data points on why that's not a viable plan in an increasingly hot and dry world. When drought hits, garden watering is the first thing that gets rationed.

Fortunately, you have plenty of options beyond municipal water. I like to rank them by cost-effectiveness - the cost per unit of water they actually provide:

Soil & vegetation → Dam/Pond → Well → Above-ground tanks → Below-ground cistern

Storing water in the soil offers the best return on investment. Through strategically placed earthworks (swales, keyline) and increased soil organic matter, you store water exactly where plants need it most. Even though there's drought in places like the UK and across the EU, there is still rainfall, but on hot, dry soil it just runs off before it soaks in, so your first lever is getting it to soak in.

Ponds and dams are the most economical way to store large quantities of water for the rest of your farming activities. This goes hand in hand with the above-mentioned earthworks. Shape the land, soak the water, harvest the surplus for later.

Wells can produce vast amounts of water relative to their cost - provided they're in the right location and drilled to the appropriate depth. I do hesitate to put it in the framework here. It’s highly dependent on your geology, topography, and location. In some locations, for example, just for a drilling rig to show up can cost over $9,000, plus there is drilling, the equipment, and installation cost. So although wells can be very effective in some cases, in others they are not, but there are other options.

Above-ground tanks give you substantial storage. There are physical and economic limits to their size; still, if you install the largest tanks your budget and space allow, you could be capturing all you need for your garden.

Below-ground cisterns are similar, but excavation costs drag down their cost-effectiveness. That’s why they are at the bottom of the list.

So here's exactly what to do this week (takes 10 minutes):

1. Multiply your garden area by the weekly watering rate: square meters × 0.025 m = cubic meters per week (1 m³ = 1,000 liters). In English units: square feet × 0.083 ft = cubic feet, then convert to gallons.
2. That's your weekly number. Double it if you're in a hot or arid region.
3. Now ask: what percentage of that currently comes out of a municipal tap? That number is your exposure.

All right, so I’m wondering what your number is, and what your backup is if the tap gets rationed? Hit reply and let me know - I read every reply.

Talk soon,

-William