Can we solve the drinking water challenges in the sewer?

The toilet flushing water serves three goals: 1: clean the bowl, 2: fill the smell-stopping syphon and 3: flush the bowl content through the sewer system. The first two goals are well served with 1.5 à 2.0 litres. The rest of the flushed volume is used for the third goal. However, the question is whether the third goal should be satisfied directly after flushing the toilet or may be postponed. In the house’s main sewer, a lot of water, originating from other streams, flushes the bowl content’ in passing by’.

The solution for excessive use of toilet flush water could consequently be simple: only use 1.5 à 2.0 litres of water to transport the bowl content to the main sewer and have this wait for the other water to pass by at another point in time. The saving may rise to 15-20% of total individual drinking water use.

This solution doesn’t require investment of invasive construction. It can be achieved by bending the rod that positions the driver in the flush tank operating the faucet. It takes some fiddling, and you must be aware of what you are doing, but every plumber or handyman can realise this variation of the classic brick in the container.

Is it that simple? It looks like it, but it deserves more consideration—for instance, assessing the flow volume in the main house sewer over time. SIMDEUM gives a comprehensive insight herein. It starts with modelling the present, well-functioning practise at the point a toilet flush enters the main sewer and measuring passing volume flows. Subsequently, comparing it with the ‘new’ situation. My educated guess is that it doesn’t make much difference, but it will take a bit longer for the content of the toilet bowl to be flushed out of the house because it has to wait till water from a shower of washing machine comes along.

It is also worthwhile to look at the toilet bowl’s hydraulic shape. We might need to optimise toilets for the reduced amount only serving the first two goals. After all, current toilet bowls have much more water available for the whole procedure.

Historically, it is more or less logical that this detailed analysis hasn’t had that much attention. The first drinking water application in the 19^th century was to serve Water Closets. Only later on we started considering goals 2 and 3. The presumption that the flushing water of the WC should perform all three functions is still actual. The detailed insight into temporal and spatial use patterns of drinking water offered by SIMDEUM, shows what happens in the sewer in much more granularity. So, it could well be that the adjustment of the toilet flush volume could fully compensate the anticipated growth of the drinking water demand. It sounds too good to be true, but it is realistic.