Cistern saver

Use a water hippo

Yep, you read that right: get yourself a hippo. But no, we’re not talking about the very un-cuddly animal, we’re talking about a water-saving device that slots neatly into your toilet cistern.

The water hippo is a small container you pop in your toilet cistern to reduce the amount of water you flush each time you pull the handle. Toilet flushing takes up more than a quarter of the water usage in an average home,1 so let’s start flushing more efficiently!

(NB this action isn't generally suitable for modern push-button style toilets - read more in the 'how' section)


Here are a few reasons to take action.

Click for more info or scroll to read them all.


Here's a thought for you while you're in the toilet: about 30% of your households water is flushed down the loo.1. That's perfectly drinkable water going down the drain.

Depending on your cistern, by installing a water saving device you can save 2 to 3 litres of water each time you flush.

The water saved by one hippo might not seem very significant (c. 15,000 litres a year - not bad really) but as with most of our Do Actions, when you add everyone's actions together, the difference is huge.


litres of water could be saved per year per toilet using a water saving device.

Energy & climate change

A fair bit of energy is required to clean the water before it is useable for consumption. Add that to the energy required to power the pump to bring it to your tap, and you see that even water has a carbon price tag. 


If you're on a water meter, this one saves you cash within weeks. You could knock £25 off your water bills per year with a single water saving device at home, or £3 per employee if installed in the workplace.3

And best of all - there's practically no up front cost involved.

Global Goals

In September 2017, a historic agreement was signed by UN member nations agreeing to work towards 17 Global Goals for Sustainable Development by 2030, otherwise known as the SDGs.

Achieving these ambitious goals will require action from governments, businesses, NGOs, and individuals alike. We can - and must - all play our part.

By making the 'Cistern saver' pledge, you are contributing to the following SDG targets:

6.4: By 2030, substantially increase water-use efficiency across all sectors and ensure sustainable withdrawals and supply of freshwater to address water scarcity and substantially reduce the number of people suffering from water scarcity.

6.b: Support and strengthen the participation of local communities in improving water and sanitation management

12.8: By 2030, ensure that people everywhere have the relevant information and awareness for sustainable development and lifestyles in harmony with nature

13.3: Improve education, awareness-raising and human and institutional capacity on climate change mitigation, adaptation, impact reduction and early warning


If your toilet flush operates via a handle, lever or chain, or was installed before 2001, it will almost certainly be using more water than needed.

Here's a few ways you can go about reducing the waste:

  1. Most water companies provide free water hippo bags straight to your doorstep. Ask them if they do.
  2. Buy your own Water Hippo on Amazon here. NB they sell two sizes - Hippo 7 for cisterns up to 9 litres, or Hippo 9 for any that are 9 litres or larger.
  3. Fashion your own water saving device using a small water bottle filled with tap water or a house brick (just make sure it’s not too crumbly, you don’t want to clog your pipes up!).

If the flush operates via a push button or if your system is dual flush, then good on you - you're already flushing as efficiently as you can; this pledge isn't for you.

Success Stories


in total



Both toilets now have hippo installed

My cistern was a newer version so did not need one

Turns out I cant fit hippos to my toilets. I did try though!

So easy and free to get a bag to put in our cistern - why wouldn't you!?

Easy to achieve by simple means

Milk bottles filled with sand................