Theoretically someone could enter Brussels for a semi-short-term (e.g. 90 days) and need water service but as a non-resident I think all banks would refuse them an account. So Vivaqua should really comply with the law¹ and accept cash.
- caveat: The most recent terms of service actually state that payments must be made by bank, so it’s unclear if they are breaking the law. I’ve heard that contracts can override law in Belgium which is strange. It would seem any merchant could simply make customers agree to pay electronically to circumvent the cash acceptance obligation.… or vice-versa.
There are a few pitfalls with that (assuming they have an account at their origin):