In February, following extensive lobbying by umbrella body SCVO, the Scottish Executive agreed to introduce reliefs and exemptions for charities on their water charges.
Organisations with an income of less than £50,000 a year would get 100 per cent relief on charges, while those with more than £50,000 would be entitled to some compensation for a hardship fund.
But with the new charges coming into force on 1 April with the creation of new water authority Scottish Water, details of the reliefs remain unknown.
SCVO's director of corporate affairs Lucy McTernan said: "SCVO regularly receives enquiries about how these charges will affect voluntary groups and charities and this delay will only increase the uncertainty. Even now the principle has been agreed to protect them. Until the details are published, many will be alarmed at the prospect of unmanageable bills."