In 1889 the railway link from Thames to Te Aroha was completed giving visitors from Auckland two travel options to the spa: by rail through Hamilton, or by boat from Auckland to Thames and from there by rail.

On Queen Victoria’s birthday, 24 May 1898 Hon. A J Cadman, Minister for Railways and Mines, opened the Cadman Bath House. The building measured 30m long by 8.5m wide with private baths and a central corridor 2.4m wide. A new band rotunda was also erected.

By the turn of the century 22 springs had been discovered in The Domain, 15 of which were hot.

However, by 1901 a general opinion prevailed that it would be in the interests of the District if the Hot Springs Domain reverted to direct Government control with management passing into the control of the Department of Tourist and Health Resorts. On 7th January 1903 by Order in Council the Government resumed control vesting the reserve in the Minister in Charge of Tourist and Health Resorts under the provisions of the Public Domains Act of 1881.

After the Domain came under the control of the Department of Tourist and Health Resorts in 1903 the administration building (now the Information Kiosk) was enlarged to provide consulting and waiting rooms and Dr George G Kenny was transferred from Rotorua as Resident Medical Officer. In addition to his official duties, which included supervision of the whole of The Domain, he was also to act as the medical practitioner for Te Aroha, there being no other doctor in town.

The science of baleanology and the importance of the hot pools for their curative purposes filled an important role at the Te Aroha spa. Reporting for the year 1905 to 1906 Dr Kenny notes the great increase in public rather than private bathing. He attributes this switch to some very large public excursions from the goldfield townships, the large majority of who preferred a warm plunge rather than a private bath, "in other words they bathed for pleasure, rather than for the relief of ailments." He thought that the opening of the Waihi Railway had also helped to bring about the change, as; "the industrial classes have largely availed themselves of the cheaper and more convenient traveling facilities, and have patronised the less expensive baths."

The Te Aroha spa continued to be as important for curative purposes as it was for recreation and enjoyment throughout the first half of the twentieth century. In 1906 massage rooms were fitted up and an operator installed, and in 1929 a new massage room was built onto the rear of the Cadman Bath House and updated X-ray equipment was installed. As late as 1950 a qualified physiotherapist was practising, providing massage and special treatments and provided 4,000 treatments in the year 1949-50.

Despite the fact that Rotorua, which was now linked into the North Island rail network, had eclipsed Te Aroha in terms of visitor numbers, the popularity of the Domain grew throughout the first decade of the nineteenth century. In January 1903 a new bowling green was opened that proved very popular and was considered one of the best in the country. The same year a grass tennis court and a croquet lawn were opened and Domain staff was increased from two bath attendants to four, and with the appointment of head gardener. In 1905 the cold swimming bath was repaired and reopened and a Bath House provided.