Use TREC Notice to purchaser of Special taxing or assessment district. TREC 59-0, TXR 1420 - 59-0
Sometimes they have their own notice documents which can be used, but normally use the TREC form for MUD notification.
As a reminder:
1) The MUD Notice must be provided before the purchase contract is executed, or attached as an addendum when the contract is signed
2) Both seller and buyer must sign and date the Notice to acknowledge its receipt
3) If the notice isn't delivered properly or on time, the buyer may terminate the contract up until closing or even sue later for damages.
The information for the MUD can be found by checking this website: https://experience.arcgis.com/experience/b5628eb1be7742c685ea589d4c93963f#data_s=id%3AdataSource_1-WaterDistricts_OperationalLayers_9314-0-6%3A236142
Zoom in on the map and click the area for the water district, then click the District Information link.
This is an example of that information. You can call their address and double verify the address of the property and get the information to fill in the MUD data for the TREC form.