According to them there are in fact 48 toilets on the Metro and the RER. Most of these, 32 in fact, are on the RER lines A and B which cross the Paris region and the centre of the capital from west to east and from north to south.

The availability of bathrooms on Paris trains depends entirely on the type of train service you are using. On the Paris Metro, there are absolutely no bathrooms on the trains, and they are also quite rare in the stations themselves. On the RER (the regional express trains that go to places like Disney or Versailles) and the Transilien (suburban commuter trains), most modern trains do not have on-board bathrooms; while some older models had them, they have largely been locked and decommissioned due to hygiene and security concerns. However, for long-distance travel on the TGV (high-speed) and Intercités trains, bathrooms are standard and generally well-maintained, located at the end of each carriage. If you are using the Metro or RER, it is highly recommended to use the facilities at major "Grandes Lignes" stations (like Gare du Nord or Gare de Lyon) before boarding, as these stations typically have paid, attended restrooms. For shorter city hops, you are expected to use the restrooms in cafes or public "Sani-vettes" on the street, as the urban rail network is designed for high-frequency, short-duration travel where on-board facilities are not a priority.