The moisture pattern
For Omothymus violaceopes, use moisture-dependent setup with deep lower substrate, good ventilation and a constant water source. Use that as a practical pattern across the enclosure instead of trying to make every part of the substrate equally wet.
Watch how quickly the Singapore Blue Tarantula enclosure changes over several days. The same amount of water behaves differently in a sling tub and a larger adult setup.
Water dish
Keep a clean water dish available to Omothymus violaceopes once the spider is large enough to use one safely. Refill it before it stays dry for long periods.
Fresh drinking water and substrate moisture serve different purposes in a Singapore Blue Tarantula enclosure; one should not be used as an excuse to ignore the other.
When the enclosure is too wet
Persistent condensation, a stale smell, widespread mould and substrate that never begins to dry are signs that the Omothymus violaceopes enclosure may be staying too wet.
If that happens with a Singapore Blue Tarantula, reduce how much water is added and improve airflow where necessary. Do not solve excess moisture by removing the water dish.
When the enclosure is too dry
If the Omothymus violaceopes substrate dries through very quickly and the species needs a moisture reserve, add water to a controlled area or use more appropriate substrate depth.
Small Singapore Blue Tarantulas can dry faster than adults, so juvenile enclosures often need more frequent checking even when the adult species is not kept damp.
Seasonal changes
UK heating in winter and warm summer rooms can change how quickly the Omothymus violaceopes enclosure dries. Adjust watering to the enclosure itself, not to a calendar.
The care target for a Singapore Blue Tarantula stays the same through the year; what changes is how quickly the room and ventilation move the setup toward drier conditions.