My Rainwater Toilet System: 5 Years & 25,000 Litres Saved

Why I Built a Rainwater Harvesting System

I have a passion for personal finance and problem-solving, and when we moved into our new house, we discovered it was on a water meter rather than the unmeasured supply typical in our area. This sparked a journey that would lead to significant water savings.

Living in Portsmouth, I quickly learned how water costs add up. Portsmouth Water charges us per cubic meter for supply, and then Southern Water charges 92.5% of that amount for wastewater treatment. That's nearly double the cost for every drop of water!

While researching ways to reduce consumption, I discovered people were storing rainwater to flush their toilets. This wasn't entirely new to us—we'd previously used a bucket of water from a waterbutt to manually flush our toilet during a mains supply issue on our street. The difference? This time, I wanted to automate the process.

In essence, this was a cost-saving exercise—but it's evolved into something more meaningful.

How the Rainwater Harvesting System Works

The setup is surprisingly straightforward once you understand the components. Here's how rainwater travels from my roof to the toilet:

The Water Collection Path

1. Roof Collection: Rainwater runs off the roof into standard gutters
2. J-Pipe First Flush: The downpipe feeds into a J-pipe that acts as a first-flush system
3. Waterbutt Storage: Debris-free water overflows into a tall freestanding waterbutt
4. Overflow Protection: Before the waterbutt overflows, water backs up into a pipe connected to the original downpipe
5. Delivery System: A flexible hose at the bottom of the waterbutt feeds through a water meter
6. Toilet Connection: The pipe travels through a wall overflow hole into the toilet cistern

The First Flush System - Critical for Water Quality

The J-pipe is one of the most important components. It collects the initial "first flush" of water that washes moss, bird droppings, and general debris off the roof. This dirty water accumulates in the J-pipe and can be emptied by opening the cap—I typically empty it into a bucket.

Gravity vs. Pump Operation

The system operates in two modes depending on water levels:

• Gravity Feed: When the waterline in the waterbutt is above the cistern inlet pipe, water flows naturally into the toilet cistern. No pump, no electricity—just gravity doing its job.
• Pump Assisted: When the water level drops below the cistern inlet, I use a 12V pump (purchased off eBay) connected via an extension cord. I typically run this on clear days to top up the system.

Safety: The Critical Air Gap

The cistern also has a mains water connection with a crucial safety feature: an air gap. This was assessed and signed off by Portsmouth Water. The air gap ensures there's absolutely no risk of contaminated rainwater entering the mains water supply.

Why is this so important? Rainwater from the roof is considered extremely dirty because it can come into contact with bird feces and other contaminants. The air gap provides physical separation between the two water sources.

This dual supply means the toilet can still be filled by mains water even if the waterbutt runs dry or drops below the cistern inlet level. It's a failsafe system that ensures the toilet always works.

Tracking Water Consumption

One of my favorite parts of this project is the water meter I installed between the waterbutt and the toilet. This £25 meter has been instrumental in tracking exactly how much rainwater I'm using— and how much money I'm saving. After 5 years, it's recorded 25,000 litres of consumption!

My Weekly Tracking Routine

Every Sunday, I take a photo of the water meter reading. When I get a chance, I log that data into a spreadsheet which has become an invaluable tool for understanding the system's performance.

My spreadsheet tracks several key metrics:

• Weekly consumption: How many litres used that week
• Cost of water: What that consumption would have cost at current water rates
• Running total of savings: Cumulative money saved over time
• Capital repayment: How much of the initial £300 investment I've recovered
• Maintenance losses: Litres lost during maintenance (e.g., cleaning the inlet float and testing by flushing)

This level of tracking might seem obsessive, but it's incredibly satisfying to see the numbers grow each week. It also helps me spot any issues—if weekly consumption suddenly drops, I know to check for blockages or problems with the system.

The Installation Process

While I planned out the entire system myself, the timing coincided with a bathroom refurbishment project. We were having the downstairs toilet refitted with leftover tiles from our previous house's bathroom, which added complexity to the installation.

Installation Photo Gallery

Here's a visual journey through the installation process:

What I Did vs. What Contractors Did

I handled the planning and tile layout, figuring out how to make the most of our leftover tiles. The contractors focused on the heavy work:

• Formed a concrete base for the waterbutt to sit on
• Secured the waterbutt to the wall with a wire brace for stability
• Installed the pipework from the guttering to the waterbutt

Perfect Timing: An Ironic First Test

The rainwater harvesting system came into use immediately after installation in the most ironic way possible. Just as we finished setting it up, there was a burst pipe in our road that interrupted the mains water supply. While our neighbors couldn't flush their toilets, ours worked perfectly using collected rainwater!

It was an unexpected but perfect demonstration of the system's value beyond just cost savings—having a backup water source for essential functions like toilet flushing provides genuine resilience during emergencies.

The Finished System

The completed rainwater harvesting system, now 5 years old and still going strong

Video: Watch the System in Action

I've created a detailed video walkthrough of the entire rainwater harvesting system, showing how it works, the installation, and discussing the costs and savings in depth. This gives you a much better visual understanding of the setup than photos alone.

The Real Costs and Savings

Initial Investment

Excluding the cost of contractor labor, here's what I spent on materials:

• Tall Freestanding Waterbutt: £275
• Water Meter: £25
• Total Material Cost: £300

The Savings Reality Check

Initially, I was very optimistic about payback time—I calculated around 5 years based on our household situation at the time. We had kids being potty trained and regular visitors using the downstairs toilet. I thought the savings would rack up quickly.

Reality was different. The upstairs toilet still gets used a lot, which I didn't fully account for in my initial projections.

After 5 years of operation:

• Water Saved: 25,000 litres
• Money Saved: £75
• Cost Recovery: 28% of the initial £300 investment

However, there's good news: rising water rates and kids being out of nappies means the system is paying for itself faster each year. The payback is accelerating.

Challenges and Solutions

Choosing the Storage Location

One of the biggest decisions was where to place the waterbutt. I considered several options:

• Underground: Would have provided more capacity and been invisible, but would have required significantly more installation effort and would have needed a pump for all operation (no gravity feed option)
• Above Ground: Easier to install and maintain, with the benefit of gravity-fed operation when full

I ultimately sourced a tall freestanding tank that could be installed in an area that's shaded year-round. The shade is important—it helps prevent algae growth and keeps the water cooler, reducing the risk of unpleasant smells.

Installation Quality Issues

As mentioned earlier, the contractors' pipework from the guttering wasn't up to my standards. The lesson here is clear: if you're paying for installation, be present and oversee the work. Don't assume contractors understand the nuances of what you're trying to achieve.

Five Years Later: How It's Working

The system is actually working fine, and for the most part, you don't notice it running in the background. It's become part of our normal household infrastructure—which is exactly what I wanted.

Active Management for Maximum Savings

Every now and again, especially during spells of wet weather, I turn off the mains water supply to the toilet cistern. This maximizes rainwater consumption and pushes my savings higher. It's a small action that makes a real difference to the monthly water bill.

Maintenance Requirements

The maintenance is minimal but important:

• Regular J-pipe emptying: Prevents stagnation and smell issues
• Occasional pump use: On clear days when water levels are low
• Mains valve management: Turning off mains during wet periods to maximize rainwater use
• Visual inspections: Checking for leaks or blockages periodically

More Than Just Money

I initially did this for the financial savings, and yes, reducing the water bill was the primary motivation. But there's something else that's become important over these five years.

We're flushing drinking water down the toilet. Think about that for a moment. Clean, treated, drinkable water that takes energy and resources to produce—and we're literally flushing it away.

Having saved 25,000 litres gives me a genuine feel-good satisfaction beyond the money. That's 25,000 litres of drinking water that's stayed in the system for actual drinking water purposes. It's a small contribution to water conservation, but it's something.

Should You Build One?

After five years of experience, here's my honest recommendation:

It Makes Sense If:

• You have a downstairs toilet on an outside wall (much easier installation)
• You're on a water meter (unmetered users won't see savings) - use this calculator to check if switching to a meter would save you money
• You can keep costs reasonable (don't overspend on elaborate setups)
• You're comfortable with basic DIY or can oversee contractors well
• You have space for above-ground storage (ideally shaded)
• You're motivated by both financial and environmental benefits

It Might Not Be Worth It If:

• Your only toilet is upstairs (much more complex installation)
• You're on an unmetered water supply (no financial incentive)
• You're quoted high installation costs (diminishing returns on investment)
• You don't have suitable outdoor space
• You're not willing to do occasional maintenance

Key Advice

Final Thoughts

Five years in, my rainwater toilet system has saved 25,000 litres of drinking water and £75 in water bills. The financial payback is slower than I initially hoped, but it's accelerating as water rates increase.

More importantly, it's working reliably in the background, requiring minimal intervention, and contributing to water conservation every single day. For me, that combination of practical functionality and environmental benefit makes it worthwhile.

If you have a downstairs toilet on an outside wall and you're on a water meter, I'd encourage you to consider it. Just keep your costs reasonable, plan carefully, and don't let contractors rush the installation!