Gross stagnant toilet water

[MsVanRein]

This is probably a bizarre issue to have as I can't work out the reason but basically over the last couple of weeks I've noticed the water in all 3 loos really seems quite whiffy and stagnant. It appears to coincide with the water level looking oddly low - I've no idea what could have caused this!?

Loos are cleaned regularly and are given a go over with toilet brush (sinful I know!) and bleach probably every other day. Any marks in the loo are dealt with at the time with disposable toilet brush thingies so the quick clean with bleach/toilet brush are literally just to freshen up.

Any idea what could be causing this it's really driving me mad!

[PurpleWithRed]

Issue with the drains? I have absolutely no expertise or knowledge but it sounds like something from Down Below is sucking down the water/burping up again rather than anything from the cistern. But I have absolutely no idea really!

[MsVanRein]

Purple actually now that you mention that there was an issue with next doors drains when we first moved in. It's really only today I've been thinking how totally bizarre it is as even during/after cleaning them I could smell something unpleasant.